Heat and moisture exchanger for a patient interface

ABSTRACT

A patient interface for supplying a flow of breathable gas to the airways of a patient may comprise a heat and moisture exchanger (HME). The HME may be positioned in a flow path of the flow of breathable gas. The HME may absorb heat and moisture from gas exhaled by the patient and the incoming flow of breathable gas to be supplied to the patient&#39;s airways may be heated and moisturized by the heat and moisture held in the HME.

1 CROSS-REFERENCE TO RELATED APPLICATIONS

his application is a continuation of U.S. Application Ser. No.15/930,597, filed May 13, 2020, now pending, which is a continuation ofU.S. application Ser. No. 14/908,280, filed Jan. 28, 2016, now U.S. Pat.No. 10,695,521, which is the U.S. national phase of InternationalApplication No. PCT/AU2014/050154 filed Jul. 29, 2014 which designatedthe U.S. and claims priority to Australian Patent Application No. AU2013902810, filed Jul. 29, 2013, and New Zealand Patent Application No.NZ 613874, filed Aug. 7, 2013, the entire contents of each of which arehereby incorporated by reference.

2 BACKGROUND OF THE TECHNOLOGY 2.1 Field of the Technology

The present technology relates to one or more of the detection,diagnosis, treatment, prevention and amelioration of respiratory-relateddisorders. In particular, the present technology relates to medicaldevices or apparatus, and their use.

2.2 Description of the Related Art

2.2.1 Human Respiratory System and its Disorders

The respiratory system of the body facilitates gas exchange. The noseand mouth form the entrance to the airways of a patient.

The airways include a series of branching tubes, which become narrower,shorter and more numerous as they penetrate deeper into the lung. Theprime function of the lung is gas exchange, allowing oxygen to move fromthe air into the venous blood and carbon dioxide to move out. Thetrachea divides into right and left main bronchi, which further divideeventually into terminal bronchioles. The bronchi make up the conductingairways, and do not take part in gas exchange. Further divisions of theairways lead to the respiratory bronchioles, and eventually to thealveoli. The alveolated region of the lung is where the gas exchangetakes place, and is referred to as the respiratory zone. See“Respiratory Physiology”, by John B. West, Lippincott Williams &Wilkins, 9th edition published 2011.

A range of respiratory disorders exist. Certain disorders may becharacterised by particular events, e.g. apneas, hypopneas, andhyperpneas.

Obstructive Sleep Apnea (OSA), a form of Sleep Disordered Breathing(SDB), is characterized by events including occlusion or obstruction ofthe upper air passage during sleep. It results from a combination of anabnormally small upper airway and the normal loss of muscle tone in theregion of the tongue, soft palate and posterior oropharyngeal wallduring sleep. The condition causes the affected patient to stopbreathing for periods typically of 30 to 120 seconds duration, sometimes200 to 300 times per night. It often causes excessive daytimesomnolence, and it may cause cardiovascular disease and brain damage.The syndrome is a common disorder, particularly in middle agedoverweight males, although a person affected may have no awareness ofthe problem. See U.S. Pat. No. 4,944,310 (Sullivan).

Cheyne-Stokes Respiration (CSR) is another form of sleep disorderedbreathing. CSR is a disorder of a patient's respiratory controller inwhich there are rhythmic alternating periods of waxing and waningventilation known as CSR cycles. CSR is characterised by repetitivede-oxygenation and re-oxygenation of the arterial blood. It is possiblethat CSR is harmful because of the repetitive hypoxia. In some patientsCSR is associated with repetitive arousal from sleep, which causessevere sleep disruption, increased sympathetic activity, and increasedafterload. See U.S. Pat. No. 6,532,959 (Berthon-Jones).

Obesity Hyperventilation Syndrome (OHS) is defined as the combination ofsevere obesity and awake chronic hypercapnia, in the absence of otherknown causes for hypoventilation. Symptoms include dyspnea, morningheadache and excessive daytime sleepiness.

Chronic Obstructive Pulmonary Disease (COPD) encompasses any of a groupof lower airway diseases that have certain characteristics in common.These include increased resistance to air movement, extended expiratoryphase of respiration, and loss of the normal elasticity of the lung.Examples of COPD are emphysema and chronic bronchitis. COPD is caused bychronic tobacco smoking (primary risk factor), occupational exposures,air pollution and genetic factors. Symptoms include: dyspnea onexertion, chronic cough and sputum production.

Neuromuscular Disease (NMD) is a broad term that encompasses manydiseases and ailments that impair the functioning of the muscles eitherdirectly via intrinsic muscle pathology, or indirectly via nervepathology. Some NMD patients are characterised by progressive muscularimpairment leading to loss of ambulation, being wheelchair-bound,swallowing difficulties, respiratory muscle weakness and, eventually,death from respiratory failure. Neuromuscular disorders can be dividedinto rapidly progressive and slowly progressive: (i) Rapidly progressivedisorders: Characterised by muscle impairment that worsens over monthsand results in death within a few years (e.g. Amyotrophic lateralsclerosis (ALS) and Duchenne muscular dystrophy (DMD) in teenagers);(ii) Variable or slowly progressive disorders: Characterised by muscleimpairment that worsens over years and only mildly reduces lifeexpectancy (e.g. Limb girdle, Facioscapulohumeral and Myotonic musculardystrophy). Symptoms of respiratory failure in NMD include: increasinggeneralised weakness, dysphagia, dyspnea on exertion and at rest,fatigue, sleepiness, morning headache, and difficulties withconcentration and mood changes.

Chest wall disorders are a group of thoracic deformities that result ininefficient coupling between the respiratory muscles and the thoraciccage. The disorders are usually characterised by a restrictive defectand share the potential of long term hypercapnic respiratory failure.Scoliosis and/or kyphoscoliosis may cause severe respiratory failure.Symptoms of respiratory failure include: dyspnea on exertion, peripheraloedema, orthopnea, repeated chest infections, morning headaches,fatigue, poor sleep quality and loss of appetite.

A range of therapies have been used to treat or ameliorate suchconditions. Furthermore, otherwise healthy individuals may takeadvantage of such therapies to prevent respiratory disorders fromarising. However, these have a number of shortcomings.

2.2.2 Therapy

Nasal Continuous Positive Airway Pressure (CPAP) therapy has been usedto treat Obstructive Sleep Apnea (OSA). The hypothesis is thatcontinuous positive airway pressure acts as a pneumatic splint and mayprevent upper airway occlusion by pushing the soft palate and tongueforward and away from the posterior oropharyngeal wall. Treatment of OSAby nasal CPAP therapy may be voluntary, and hence patients may elect notto comply with therapy if they find devices used to provide such therapyone or more of uncomfortable, difficult to use, expensive oraesthetically unappealing.

Non-invasive ventilation (NIV) provides ventilatory support to a patientthrough the upper airways to assist the patient in taking a full breathand/or maintain adequate oxygen levels in the body by doing some or allof the work of breathing. The ventilatory support is provided via apatient interface. NIV has been used to treat CSR, OHS, COPD, MD andChest Wall disorders. In some forms, the comfort and effectiveness ofthese therapies may be improved.

Invasive ventilation (IV) provides ventilatory support to patients thatare no longer able to effectively breathe themselves and may be providedusing a tracheostomy tube. In some forms, the comfort and effectivenessof these therapies may be improved.

2.2.3 Diagnosis and Treatment Systems

These therapies may be provided by a treatment system or device. Systemsand devices may also be used to diagnose a condition without treatingit.

A treatment system may comprise a Respiratory Pressure Therapy Device(RPT device), an air circuit, a humidifier, a patient interface, anddata management.

Another form of treatment system is a mandibular repositioning device.

2.2.3.1 Patient Interface

A patient interface may be used to interface respiratory equipment toits user, for example by providing a flow of air. The flow of air may beprovided via a mask to the nose and/or mouth, a tube to the mouth or atracheostomy tube to the trachea of the user. Depending upon the therapyto be applied, the patient interface may form a seal, e.g. with a faceregion of the patient, to facilitate the delivery of gas at a pressureat sufficient variance with ambient pressure to effect therapy, e.g. apositive pressure of about 10 cmH2O. For other forms of therapy, such asthe delivery of oxygen, the patient interface may not include a sealsufficient to facilitate delivery to the airways of a supply of gas at apositive pressure of about 10 cmH2O.

The design of a patient interface presents a number of challenges. Theface has a complex three-dimensional shape. The size and shape of nosesvaries considerably between individuals. Since the head includes bone,cartilage and soft tissue, different regions of the face responddifferently to mechanical forces. The jaw or mandible may move relativeto other bones of the skull. The whole head may move during the courseof a period of respiratory therapy.

As a consequence of these challenges, some masks suffer from being oneor more of obtrusive, aesthetically undesirable, costly, poorly fitting,difficult to use, and uncomfortable especially when worn for longperiods of time or when a patient is unfamiliar with a system. Forexample, masks designed solely for aviators, mask designed as part ofpersonal protection equipment (e.g. filter masks), SCUBA masks, or forthe administration of anaesthetics may be tolerable for their originalapplication, but nevertheless be undesirably uncomfortable to be wornfor extended periods of time, e.g. several hours. This discomfort maylead to a reduction in patient compliance with therapy. This is evenmore so if the mask is to be worn during sleep.

Nasal CPAP therapy is highly effective to treat certain respiratorydisorders, provided patients comply with therapy. If a mask isuncomfortable, or difficult to use a patient may not comply withtherapy. Since it is often recommended that a patient regularly washtheir mask, if a mask is difficult to clean (e.g. difficult to assembleor disassemble), patients may not clean their mask and this may impacton patient compliance.

While a mask for other applications (e.g. aviators) may not be suitablefor use in treating sleep disordered breathing, a mask designed for usein treating sleep disordered breathing may be suitable for otherapplications.

For these reasons, patient interfaces for delivery of nasal CPAP duringsleep form a distinct field.

2.2.3.1.1 Seal-Forming Portion

Patient interfaces may include a seal-forming portion. Since it is indirect contact with the patient's face, the shape and configuration ofthe seal-forming portion can have a direct impact the effectiveness andcomfort of the patient interface.

A patient interface may be partly characterised according to the designintent of where the seal-forming portion is to engage with the face inuse. In one form of patient interface, a seal-forming portion maycomprise two sub-portions to engage with respective left and rightnares. In one form of patient interface, a seal-forming portion maycomprise a single element that surrounds both nares in use. Such singleelement may be designed to for example overlay an upper lip region and anasal bridge region of a face. In one form of patient interface aseal-forming portion may comprise an element that surrounds a mouthregion in use, e.g. by forming a seal on a lower lip region of a face.In one form of patient interface, a seal-forming portion may comprise asingle element that surrounds both nares and a mouth region in use.These different types of patient interfaces may be known by a variety ofnames by their manufacturer including nasal masks, full-face masks,nasal pillows, nasal puffs and oro-nasal masks.

A seal-forming portion that may be effective in one region of apatient's face may be inappropriate in another region, e.g. because ofthe different shape, structure, variability and sensitivity regions ofthe patient's face. For example, a seal on swimming goggles thatoverlays a patient's forehead may not be appropriate to use on apatient's nose.

Certain seal-forming portions may be designed for mass manufacture suchthat one design fit and be comfortable and effective for a wide range ofdifferent face shapes and sizes. To the extent to which there is amismatch between the shape of the patient's face, and the seal-formingportion of the mass-manufactured patient interface, one or both mustadapt in order for a seal to form.

One type of seal-forming portion extends around the periphery of thepatient interface, and is intended to seal against the user's face whenforce is applied to the patient interface with the seal-forming portionin confronting engagement with the user's face. The seal-forming portionmay include an air or fluid filled cushion, or a moulded or formedsurface of a resilient seal element made of an elastomer such as arubber. With this type of seal-forming portion, if the fit is notadequate, there will be gaps between the seal-forming portion and theface, and additional force will be required to force the patientinterface against the face in order to achieve a seal.

Another type of seal-forming portion incorporates a flap seal of thinmaterial so positioned about the periphery of the mask so as to providea self-sealing action against the face of the user when positivepressure is applied within the mask. Like the previous style of sealforming portion, if the match between the face and the mask is not good,additional force may be required to effect a seal, or the mask mayunintentionally leak. Furthermore, if the shape of the seal-formingportion does not match that of the patient, it may crease or buckle inuse, giving rise to unintentional leaks.

Another type of seal-forming portion may comprise a friction-fitelement, e.g. for insertion into a naris, however some patients findthese uncomfortable.

Another form of seal-forming portion may use adhesive to effect a seal.Some patients may find it inconvenient to constantly apply and remove anadhesive to their face.

A range of patient interface seal-forming portion technologies aredisclosed in the following patent applications, assigned to ResMedLimited: WO 1998/004,310; WO 2006/074,513; WO 2010/135,785.

One form of nasal pillow is found in the Adam Circuit manufactured byPuritan Bennett. Another nasal pillow, or nasal puff is the subject ofU.S. Pat. No. 4,782,832 (Trimble et al.), assigned to Puritan-BennettCorporation.

ResMed Limited has manufactured the following products that incorporatenasal pillows: SWIFT nasal pillows mask, SWIFT II nasal pillows mask,SWIFT LT nasal pillows mask, SWIFT FX nasal pillows mask and LIBERTYfull-face mask. The following patent applications, assigned to ResMedLimited, describe nasal pillows masks: International Patent ApplicationWO2004/073,778 (describing amongst other things aspects of ResMed SWIFTnasal pillows), US Patent Application 2009/0044808 (describing amongstother things aspects of ResMed SWIFT LT nasal pillows); InternationalPatent Applications WO 2005/063,328 and WO 2006/130,903 (describingamongst other things aspects of ResMed LIBERTY full-face mask);International Patent Application WO 2009/052,560 (describing amongstother things aspects of ResMed SWIFT FX nasal pillows).

2.2.3.1.2 Positioning and Stabilising

A seal-forming portion of a patient interface used for positive airpressure therapy is subject to the corresponding force of the airpressure to disrupt a seal. Thus a variety of techniques have been usedto position the seal-forming portion, and to maintain it in sealingrelation with the appropriate portion of the face.

One technique is the use of adhesives. See for example US Patentpublication US 2010/0000534. However these may be uncomfortable forsome.

Another technique is the use of one or more straps and stabilisingharnesses. Many such harnesses suffer from being one or more ofill-fitting, bulky, uncomfortable and awkward to use.

2.2.3.1.3 Vent Technologies

Some forms of patient interface systems may include a vent to allow thewashout of exhaled carbon dioxide. The vent may allow a flow of gas froman interior space of the patient interface, e.g. the plenum chamber, toan exterior of the patient interface, e.g. to ambient. The vent maycomprise an orifice and gas may flow through the orifice in use of themask. Many such vents are noisy. Others may block in use and provideinsufficient washout. Some vents may be disruptive of the sleep ofabed-partner 1100 of the patient 1000, e.g. through noise or focusedairflow.

ResMed Limited has developed a number of improved mask venttechnologies. See WO 19981034,665; WO 2000/078,381; U.S. Pat. No.6,581,594; US Patent Application; US 2009/0050156; US Patent Application2009/0044808.

Table of noise of prior masks (ISO 17510-2:2007, 10 cm H₂O pressure at 1m) A-weighted A-weighted sound power sound pressure level dB(A) dB(A)Year Mask name Mask type (uncertainty) (uncertainty) (approx.) Glue-on(*) nasal 50.9 42.9 1981 ResCare nasal 31.5 23.5 1993 standard (*)ResMed nasal 29.5 21.5 1998 Mirage (*) ResMed nasal 36 (3) 28 (3) 2000UltraMirage ResMed nasal 32 (3) 24 (3) 2002 Mirage Activa ResMed nasal30 (3) 22 (3) 2008 Mirage Micro ResMed nasal 29 (3) 22 (3) 2008 MirageSoftGel ResMed nasal 26 (3) 18 (3) 2010 Mirage FX ResMed nasal pillows37 29 2004 Mirage Swift (*) ResMed nasal pillows 28 (3) 20 (3) 2005Mirage Swift II ResMed nasal pillows 25 (3) 17 (3) 2008 Mirage Swift LT(* one specimen only, measured using test method specified in ISO3744 inCPAP mode at 10 cm H₂O)

Sound pressure values of a variety of objects are listed below

A-weighted sound Object pressure dB(A) Notes Vacuum cleaner: Nilfisk 68ISO3744 at 1 m Walter Broadly Litter Hog: B+ distance GradeConversational speech 60 1 m distance Average home 50 Quiet library 40Quiet bedroom at night 30 Background in TV studio 20

2.2.3.2 Respiratory Pressure Therapy (RPT) Device

Air pressure generators are known in a range of applications, e.g.industrial-scale ventilation systems. However, air pressure generatorsfor medical applications have particular requirements not fulfilled bymore generalised air pressure generators, such as the reliability, sizeand weight requirements of medical devices. In addition, even devicesdesigned for medical treatment may suffer from shortcomings, includingone or more of comfort, noise, ease of use, efficacy, size, weight,manufacturability, cost, and reliability.

An example of the special requirements of certain RPT devices isacoustic noise.

Table of noise output levels of prior RPT devices (one specimen only,measured using test method specified in ISO3744 in CPAP mode at 10cmH₂O).

A-weighted sound power Year RPT Device name level dB(A) (approx.)C-Series Tango 31.9 2007 C-Series Tango with Humidifier 33.1 2007 S8Escape II 30.5 2005 S8 Escape II with H4i Humidifier 31.1 2005 S9AutoSet 26.5 2010 S9 AutoSet with H5i Humidifier 28.6 2010

One known RPT device used for treating sleep disordered breathing is theS9 Sleep Therapy System, manufactured by ResMed. Another example of anRP device is a ventilator. Ventilators such as the ResMed Stellar™Series of Adult and Paediatric Ventilators may provide support forinvasive and non-invasive non-dependent ventilation for a range ofpatients for treating a number of conditions such as but not limited toNMD, OHS and COPD.

The ResMed Elisde™ 150 ventilator and ResMed VS III™ ventilator mayprovide support for invasive and non-invasive dependent ventilationsuitable for adult or paediatric patients for treating a number ofconditions. These ventilators provide volumetric and barometricventilation modes with a single or double limb circuit. RPT devicestypically comprise a pressure generator, such as a motor-driven bloweror a compressed gas reservoir, and are configured to supply a flow ofair to the airway of a patient. In some cases, the flow of air may besupplied to the airway of the patient at positive pressure. The outletof the RPT device is connected via an air circuit to a patient interfacesuch as those described above.

2.2.3.3 Humidifier

Delivery of a flow of air without humidification may cause drying ofairways. The use of a humidifier with a RPT device and the patientinterface produces humidified gas that minimizes drying of the nasalmucosa and increases patient airway comfort. In addition in coolerclimates, warm air applied generally to the face area in and about thepatient interface is more comfortable than cold air. A range ofartificial humidification devices and systems are known, however theymay not fulfil the specialised requirements of a medical humidifier.

Medical humidifiers are used to increase humidity and/or temperature ofthe flow of air in relation to ambient air when required, typicallywhere the patient may be asleep or resting (e.g. at a hospital). As aresult, a medical humidifier may be small for bedside placement, and itmay be configured to only humidify and/or heat the flow of air deliveredto the patient without humidifying and/or heating the patient'ssurroundings. Room-based systems (e.g. a sauna, an air conditioner, anevaporative cooler), for example, may also humidify air that is breathedin by the patient, however they would also humidify and/or heat theentire room, which may cause discomfort to the occupants. Furthermoremedical humidifiers may have more stringent safety constraints thanindustrial humidifiers

While a number of medical humidifiers are known, they can suffer fromone or more shortcomings. Some medical humidifiers may provideinadequate humidification, some are difficult or inconvenient to use bypatient.

2.2.4 Heat and Moisture Exchanger (HME)

Heat and moisture exchangers are generally made up of foam, paper, or asubstance capable of acting as a condensation and absorption surface.The material may carry hygroscopic salts to improve the water-retainingcapacity. Suitable salts include calcium chloride.

HMEs may be utilized in RPT therapy, such as in PAP therapy, topartially recover heat and moisture present in exhaled gas from apatient's airways. This heat and moisture can be retained and recycledto the patient in a passive manner as a flow of breathable gas passesthrough the HME prior to inspiration. Thus, the use of HME's can providethe needed moisture and humidity (generally recognized as >10 mg/l) tomost patients during PAP therapy to minimize any detrimental effectsassociated with PAP therapy with non-humidified ambient air whilstavoiding the need for a heated humidifier system. The use of a HMErather than a heated humidifier may also lower the possibility ofocclusion caused by condensation in air delivery tubes.

The use of a HME in PAP therapy can avoid the need for additional powerrequired with heated humidifiers and may reduce the need for extraassociated components. This may reduce the manufacturing costs and alsoreduce the overall size of the CPAP therapy unit.

A problem common with the use of HMEs in CPAP therapy relates to theability of the HME to provide sufficient heat and moisture while alsominimizing flow impedance and maintaining comfortable and safe levels ofCO2 washout. Flow impedance may affect patient breathing effort (work ofbreathing) and also impacts event (apnoea, hypopnoea, snore) detectionalgorithms so in many cases it is sought to be minimized. Furthermore,consideration should also be given to heat and moisture loss fromventing to ensure that the HME is functioning to counteract this loss.

Current configurations of HME's in RPT therapy have shown negligiblepatient humidification, have issues with flow impedance, and/or CO₂washout. For example, placing the HME unit within the elbow, around theexhaust vent or on the flow generator side of the therapy system hasshown issues with impedance, and/or CO₂ washout with negligible patienthumidification (hygroscopic) benefit. In this configuration the ventflow is the dominant flow through the HME. The vent flow being the flowfrom the patient or the flow generator that flows through the HME anddirectly out through the vent. Moreover, current designs of HME's do notallow for sufficient moisture exchange during patient exhalation toprovide sufficient humidification levels to the patient. Thus, there isa need to provide superior configurations and designs for HME use in RPTtherapy, such as PAP therapy, to achieve desired patient humidificationwhilst having acceptable impedance on the flow of therapy and CO₂washout.

3 BRIEF SUMMARY OF THE TECHNOLOGY

The present technology is directed towards providing medical devicesused in the diagnosis, amelioration, treatment, or prevention ofrespiratory disorders having one or more of improved comfort, cost,efficacy, ease of use and manufacturability.

A first aspect of the present technology relates to apparatus used inthe diagnosis, amelioration, treatment or prevention of a respiratorydisorder.

Another aspect of the present technology relates to methods used in thediagnosis, amelioration, treatment or prevention of a respiratorydisorder.

One form of the present technology comprises a patient interface fordelivering a flow of breathable gas to an entrance of a patient'sairways including at least an entrance of a patient's nares, saidpatient interface comprising a HME comprising at least one corrugatedstructure. The corrugated structure may comprise a plurality ofcorrugations or flutes through the HME along a surface of the corrugatedstructure, wherein the corrugated structure retains moisture from a flowof expiratory gas, and wherein the retained moisture is provided to theflow of breathable gas for humidification. Moisture may include bothliquid and vapour forms. The term ‘corrugation’ as referred to here isalso commonly referred to as a flute and is used interchangeably. Theplurality of corrugations increase the surface area of the corrugatedstructure within a fixed volume, which allows for an increasedinteraction between the surface of the HME and the air exhaled from thepatient. This allows for increased heat and moisture exchange betweenthe patient and the HME and ultimately may improve the humidificationperformance of the HME within the patient interface to the desiredlevel. Furthermore, the increased humidification performance allows asmaller HME to function to a desired performance level, therebyoccupying a smaller volume in the patient interface. The volume occupiedby the HME can influence flow impedance, effecting CO₂ washout and/orresulting in therapeutic pressure loss delivered to the patient duringPAP therapy. Thus, having an increased surface area per unit volume ofthe corrugated HME material for moisture exchange allows for a reductionon the impact of the HME on flow impedance. Moreover, the corrugationsallow for greater access of the flow of breathable gas to the heat andmoisture exchange surfaces of the HME thereby providing a HME with ahigh surface area per unit volume that is capable of providing superiorhumidification to the patient.

Another aspect of one form of the present technology is the HME, whereinthe HME is orientated such that a plurality of channels defined,partially or completely, by the corrugations of the HME aresubstantially parallel to the flow path of the flow of breathable gas.The orientation of the channels allows for the flow of breathable gas toflow directly through the HME along the surface of the moisture exchangelayer, thereby reducing the impact of the HME on flow impedance.

Another aspect of one form the present technology is a HME that mayfurther comprise a substantially planar base structure, and wherein thecorrugated structure may be engaged to the base structure to form alayer. The corrugated structure may comprise an upper and a lower foldedportion and each lower folded portion may be engaged to the basestructure. The base structure may form a supporting planar base in whichthe corrugated structure may extend vertically therefrom to form thelayer. Alternatively, the layer may further comprise a substantiallyplanar top structure such that the corrugated structure is disposedbetween the top and base structures to form a concertina layer. The HMEmay be comprised of the single concertina layer. The top and basestructures may provide structural support to the corrugated structureand maintain the channels formed by the corrugations to allow the flowof breathable gas through the HME along a surface of the corrugatedstructure. The top and/or base structure may be formed of a moisturenon-absorbent material. Alternatively, the top and/or base structure maybe formed of the same material as the corrugated structure. The weightof the top and/or base structure may be between 15-100 g/m². Thethickness of the top and/or base structure impacts the rigidity of thestructures and hence their ability to provide structural support.However, there is a trade-off that exists between maximising thethickness of the top and/or base structure to provide support andminimising the thickness to reduce the impact of the HME of flowimpedance. The overall thickness of the HME is a crucial factor thatalters the density and surface area per unit volume of the HME. Thesefactors in turn impact on the overall humidification performance of saidHME.

In another form of the present technology, the HME may be formed of aplurality of layers forming a predetermined three-dimensional shapeadapted to fit within a plenum chamber of the patient interface. Eachlayer comprises a corrugated structure and at least a supportingsubstantially planar base structure. Patient interfaces come in varyingshapes and sizes. Thus, the HME must conform to the varying inner volumeof the patient interface in order to fit within its inner walls. Shapinga HME into a desired three-dimensional shape to fit within a patientinterface in the appropriate orientation is difficult. Moreover, havingthe HME fit in the correct orientation while maintaining its efficacy inhumidification and reducing the impact of the HME on flow impedance addsa further level of complexity. Generally, materials used in themanufacture of HME's cannot be moulded to produce the desiredthree-dimensional shapes while maintaining the ability to humidify theflow of gas. Thus, forming a HME from a plurality of layers in a desiredthree-dimensional shape may provide flexibility in shaping the HME whilemaintaining its humidification performance. The HME of the presenttechnology may be formed by stacking the plurality of layers. The layersmay be vertically stacked along a vertical axis of the HME. Stackinglayers of HME material allows the HME to be formed into the desiredthree-dimensional shape while positioning each layer in the appropriateorientation to maximise performance. The plurality of channels formed bythe corrugated structures within each layer may be substantiallyvertically aligned to the plurality of channels of a corrugatedstructure in an adjacent layer to maximise the flow of breathable gasthrough the channels for moisture exchange. Each layer may be formed bylaser cutting portions thereof to shape the layer into a predeterminedthree-dimensional shape. Alternatively, the whole HME may be shaped bylaser cutting it to a predetermined three-dimensional shape. The layersmay also be formed from different sizes and/or shapes and combined toform a HME of overall desired three-dimensional shape. Having layers ofdifferent sizes and shapes allows the formation of the HME intoirregular shapes to fit within the plenum chamber of a patientinterface.

In another form of the present technology, the HME may also be shaped toavoid contact with a patient's face. The HME may comprise an inwardlycurved portion to avoid contact with the patient's nose or mouth.Positioning, the HME in close proximity to the entrance of a patient'sairways ensures that the capture of expired moisture is maximised.However, contact to a patient's face should be avoided or at leastminimised to prevent discomfort. Thus, it is desirable to shape the HMEto follow the facial profile of a patient to position the HME in closeproximity to the entrance of a patient's airways while avoiding or atleast minimising contact with the patient. For example, the HME may becurved to follow and avoid the profile of the patient's face within thepatient interface.

In another form of the present technology, the HME is structured to havea predetermined surface area per unit volume of between 4-14 m²/m³. Thesurface area per unit volume is directly correlated to thehumidification performance of the HME. That is, having a high surfacearea per unit volume allows for an increased moisture exchange betweenthe HME and the source of humidity to capture moisture. Furthermore, anHME with a high surface area per unit volume allows for the minimisationof volume the HME occupies within the plenum chamber. The volumeoccupied by the HME within the plenum chamber can influence flowimpedance, effecting CO2 washout and therapeutic pressure delivery tothe patient. Thus, having a HME with a high surface area per unit volumeallows for a reduced impact of the HME on flow impedance. One way toreduce the surface area per unit volume is to introduce corrugationswithin the HME. Furthermore, the HME may be formed in a plurality oflayers, wherein each of the layers comprises a corrugated structure. Thecorrugated structures form a plurality of channels and allow the flow ofbreathable gas through the channels along a surface of the HME. Ineffect, the corrugations and channels increase a surface area per unitvolume of the HME.

In another form of the present technology, the HME is selected to have awater absorbency rate of between 50-100 mm/10 min. A faster waterabsorbency rate allows for faster moisture exchange by the HME. Thisallows for an overall improved moisture uptake by the HME andsubsequently faster moisture redelivery from the HME to the patient. Thewater absorbency rate may be modified by altering the amount of HMEmaterial available within a fixed volume. Moreover, the water absorbencyrate is also impacted by the surface area of the HME that is availablefor moisture exchange. Thus, the HME may be selected to maximise theamount of HME material within a predetermined volume, while trying tomaximise the surface area per unit volume of the HME available formoisture exchange. Moreover, the water absorbency rate may also beincreased by the addition of biocompatible additives such as dryingadditives. For example, CaCl₂) may be added to the HME.

Another aspect of one form of the present technology is directed towardsa HME structured to have a flow impedance of between 0-2.5 cm of H₂O ata predetermined flow rate of 100 L/min. The flow impedance may bebetween 0-1.6 cm of H₂O at the predetermined flow rate. The flow rate isthe flow of breathable gas delivered to the patient interface. The HMEcomprising at least one corrugated structure comprising a plurality ofcorrugations, the plurality of corrugations forming a plurality ofchannels to allow the flow of breathable gas through the HME along asurface of the corrugated structure. The plurality of channels mayreduce the flow impedance of the HME on the flow of breathable gas tothe predetermined flow impedance level. The plurality of channels mayalso reduce the sheet density of the corrugated structure to apredetermined sheet density to reduce the flow impedance to within thepredetermined range. The HME may be structured to have at least onecorrugated structure having a predetermined density of between 0.02-0.4g/cm³. Moreover, the obstruction may be reduced by increasing the numberof channels to a predetermined number. The flow impedance may also bereduced to within the predetermined range by increasing the pitch ofeach corrugation or flute to between 1 to 4 mm. Pitch may be understoodto mean the width of a channel defined by the corrugations. The pitch ofeach corrugation or flute is between 1.7-3.5 mm. The flow impedance mayalso be decreased to within the desired range by increasing a totalvolume of the plurality of channels in a flow path of the flow ofbreathable gas. It may also be advantageous to reduce the flow impedanceof the HME to the flow of expiratory gas to allow a level of CO₂ washoutfrom the patient interface sufficient to prevent significant inspirationof CO₂ that may cause breathing discomfort. It is however, alsodesirable to maintain the humidification performance of the HME on theflow of breathable gas to increase breathing comfort. To increasehumidification performance to a predetermined level may require aminimum amount of HME material be present within the HME. Thus, abalance is desirable between the reduction on the level of flowimpedance on the flow of expiratory gas caused by the HME and itsmaintenance of humidification performance.

Another aspect of one form of the present technology is directed towardsa HME for removable engagement to a patient interface for delivery of aflow of breathable gas to an entrance of a patient's airways includingat least an entrance of a patient's nares, wherein the HME may comprisea rigid frame circumferentially surrounding a peripheral surface of theHME, wherein the frame may be configured to removably engage to an innersurface of a plenum chamber of the patient interface to position the HMEin a flow path of the flow of breathable gas. The rigid HME frame mayprovide structural support to the HME and provide a removably engageableportion to engage within the patient interface. The rigid framecomprises at least one engaging member for engaging to an inner surfaceof a plenum chamber of the patient interface. The engaging member maycomprise a clip for engaging to an inner surface of the plenum chamber.Alternatively, the engaging member may be in the form selected from agroup consisting of an adhesively engageable portion, a clip, aresilient flange, a hook and a loop.

Another aspect of one form of the present technology is directed towardsthe HME frame further comprising a moisture retaining reservoir toretain and resupply additional moisture to the HME material of the HME.For example, the reservoir may resupply the retained moisture to a layerof the HME. In addition to the retention of moisture by the HME, anadditional reservoir for retaining moisture may be provided to theframe. For example, a portion of the HME frame may be formed by amoisture absorbent material. This material may be a high density sponge.Moisture can be wicked by the high density sponge frame from the HME andresupplied to the HME to provide supplemental moisture.

Another aspect of one form of the present technology is directed towardsa patient interface for delivery of a flow of breathable gas to anentrance of a patient's airways including at least an entrance of apatient's nares, said patient interface comprising a HME configured toseparate a plenum chamber of the patient interface into a first anteriorchamber and a second posterior chamber. The HME may be positioned in theplenum chamber to humidify the flow of breathable gas flowing from thefirst anterior chamber to the second posterior chamber. The secondposterior chamber may comprise a seal-forming structure for sealing on aportion of the patient's face. The first anterior chamber may comprisean inlet for receiving the flow of breathable gas into the firstanterior chamber and a vent for washout of the flow of expiratory gasfrom the first anterior chamber. This position of the HME in thisconfiguration may be advantageous as it ensures that expiratory gasesfrom a patient flow through the HME for moisture retention prior towashing out through the vent. In addition, the HME may be positioned toensure that the flow of breathable gas flowing from the inlet flowsthrough the HME to redeliver the retained moisture to the patient.Alternatively, it is also possible to position an additional vent in theposterior plenum chamber to offset CO₂ build up within this volume. Forexample, in the case of a full face mask, the additional volume in theposterior plenum chamber (i.e., dead space volume) in comparison tosmaller masks may lead to unwanted excessive CO₂ build up occurringwithin this space. To mitigate this effect, it is possible to positionan additional vent proximal to the patient's airways, on the posterioror patient side of the plenum chamber relative to the HME. Positioning avent on the posterior side of the HME may aid in venting of the HMEhumidified flow of breathable gases prior to delivery to the patient. Tocompensate for this venting of humidified air, the overallhumidification performance may be maintained by increasing the abilityof the HME to humidify the flow of breathable gas within a predeterminedvolume of the plenum chamber. The inlet may be adapted to removablyengage to a conduit for the delivery of the flow of breathable gas intothe inlet. The vent may be configured for regulating the washout ofexpiratory gas at a substantially constant flow rate. The patientinterface may further comprise a vent adaptor comprising the vent andthe inlet. The vent adaptor may also be adapted to detachably engage tothe remainder of the patient interface to form the plenum chamber. Thevent adaptor may removably engage to the remainder of the patientinterface by resilient clips. The anterior portion of the vent adaptormay also form at least one wall of the first anterior chamber. The ventadaptor may comprise walls forming a housing portion for housing theHME. The housing portion may be configured to locate the HME into theplenum chamber. The vent adaptor may ensure that the vent and inlet arepositioned on an anterior side of the HME while the entrance of thepatient's airways may be positioned on a posterior side of the HME inuse. The patient interface also may comprise a cushion assemblycomprising the aperture and the seal forming structure.

Another aspect of one form of the present technology is a method ofmanufacturing a HME for humidifying a flow of breathable gas deliveredby a patient interface, the HME having a desired flow impedance. Themethod comprising corrugating at least one portion of the HME to form aplurality of channels to allow the flow of breathable gases through theHME and along a surface of the corrugated structure and adjusting thenumber of corrugations forming channels to increase a flow rate of theflow of breathable gas through the channels to achieve the desired flowimpedance.

Another aspect of one form of the present technology is a method ofmanufacturing a patient interface for delivering a flow of breathablegas to an entrance of a patient's airways, the patient interfacecomprising a HME with a desired humidification performance forhumidifying a flow of breathable gas. The method may further comprisemanufacturing a patient interface, determining the volume of a plenumchamber of the patient interface for delivering a flow of breathable gasto a patient, corrugating at least one portion of the HME to form aplurality of channels to allow the flow of breathable gases through theHME and along a surface of the corrugated structure, adjusting thenumber of corrugations forming channels to increase a surface area perunit of the HME based on the volume of the plenum chamber to achieve thedesired added absolute humidity, and/or removably or permanently fixingthe HME to within the plenum chamber of the patient interface in a flowpath of the flow of breathable gas.

Another aspect of one form of the present technology is a method ofmanufacturing a HME with an increased surface area per unit volume toachieve a desired humidification performance for humidifying a flow ofbreathable gas, the method may comprise determining the desiredhumidification performance, corrugating at least one portion of the HMEto form a plurality of channels to allow the flow of breathable gasesthrough the HME and along a surface of the corrugated structure,adjusting the number of corrugations forming channels to increase asurface area per unit volume of the HME, and/or stacking the HME intocorrugated layers to further increase a surface area per unit volume ofthe HME to achieve the desired humidification performance.

Another aspect of one form of the present technology is a method ofmanufacturing for increasing the humidification performance of a HME tohumidify a flow of breathable gas delivered by a patient interface to adesired level, the method may comprise determining the requiredhumidification performance of the HME, laser cutting a plurality ofchannels through the HME to increase a surface area per unit volume toincrease the humidification performance of the HME, and/or increasingthe number of channels by laser cutting until the desired humidificationperformance is achieved.

Another aspect of one form of the present technology is a patientinterface that is moulded or otherwise constructed with a clearlydefined perimeter shape which is intended to match that of an intendedwearer.

An aspect of one form of the present technology is a portable RPT devicethat may be carried by a person, e.g. around the home of the person.

An aspect of one form of the present technology is a patient interfacethat may be washed in a home of a patient, e.g. in soapy water, withoutrequiring specialised cleaning equipment. An aspect of one form of thepresent technology is a humidifier tank that may be washed in a home ofa patient, e.g. in soapy water, without requiring specialised cleaningequipment.

Of course, portions of the aspects may form sub-aspects of the presenttechnology. Also, various ones of the sub-aspects and/or aspects may becombined in various manners and also constitute additional aspects orsub-aspects of the present technology.

Other features of the technology will be apparent from consideration ofthe information contained in the following detailed description,abstract, drawings and claims.

4 BRIEF DESCRIPTION OF THE DRAWINGS

The present technology is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings, in whichlike reference numerals refer to similar elements including:

4.1 Treatment Systems

FIG. 1A shows a system including a patient 1000 wearing a patientinterface 3000, in the form of a nasal pillows, receives a supply of airat positive pressure from a RPT device 4000. Air from the RPT device ishumidified in a humidifier 5000, and passes along an air circuit 4170 tothe patient 1000. A bed partner 1100 is also shown.

FIG. 1B shows a system including a patient 1000 wearing a patientinterface 3000, in the form of a nasal mask, receives a supply of air atpositive pressure from a RPT device 4000. Air from the RPT device ishumidified in a humidifier 5000, and passes along an air circuit 4170 tothe patient 1000.

FIG. 1C shows a system including a patient 1000 wearing a patientinterface 3000, in the form of a full-face mask, receives a supply ofair at positive pressure from a RPT device 4000. Air from the RPT deviceis humidified in a humidifier 5000, and passes along an air circuit 4170to the patient 1000.

FIG. 1D shows a patient 1000 undergoing polysomnography (PSG).

4.2 Respiratory System and Facial Anatomy

FIG. 2A shows an overview of a human respiratory system including thenasal and oral cavities, the larynx, vocal folds, oesophagus, trachea,bronchus, lung, alveolar sacs, heart and diaphragm.

FIG. 2B shows a view of a human upper airway including the nasal cavity,nasal bone, lateral nasal cartilage, greater alar cartilage, nostril,lip superior, lip inferior, larynx, hard palate, soft palate,oropharynx, tongue, epiglottis, vocal folds, oesophagus and trachea.

FIG. 2C is a front view of a face with several features of surfaceanatomy identified including the lip superior, upper vermilion, lowervermilion, lip inferior, mouth width, endocanthion, a nasal ala,nasolabial sulcus and cheilion. Also indicated are the directionssuperior, inferior, radially inward and radially outward.

FIG. 2D is a side view of a head with several features of surfaceanatomy identified including glabella, sellion, pronasale, subnasale,lip superior, lip inferior, supramenton, nasal ridge, alar crest point,otobasion superior and otobasion inferior. Also indicated are thedirections superior & inferior, and anterior & posterior.

FIG. 2E is a further side view of a head. The approximate locations ofthe Frankfort horizontal and nasolabial angle are indicated. The coronalplane is also indicated.

FIG. 2F shows a base view of a nose with several features identifiedincluding naso-labial sulcus, lip inferior, upper Vermilion, naris,subnasale, columella, pronasale, the major axis of a naris and thesagittal plane.

FIG. 2G shows a side view of the superficial features of a nose.

FIG. 2H shows subcutaneal structures of the nose, including lateralcartilage, septum cartilage, greater alar cartilage, lesser alarcartilage, sesamoid cartilage, nasal bone, epidermis, adipose tissue,frontal process of the maxilla and fibrofatty tissue.

FIG. 2I shows a medial dissection of a nose, approximately severalmillimeters from a sagittal plane, amongst other things showing theseptum cartilage and medial crus of greater alar cartilage.

FIG. 2J shows a front view of the bones of a skull including thefrontal, nasal and zygomatic bones. Nasal concha are indicated, as arethe maxilla, and mandible.

FIG. 2K shows a lateral view of a skull with the outline of the surfaceof a head, as well as several muscles. The following bones are shown:frontal, sphenoid, nasal, zygomatic, maxilla, mandible, parietal,temporal and occipital. The mental protuberance is indicated. Thefollowing muscles are shown: digastricus, masseter, sternocleidomastoidand trapezius.

FIG. 2L shows an anterolateral view of a nose.

4.3 Patient Interface

FIG. 3A shows a patient interface in the form of a nasal mask inaccordance with one form of the present technology.

4.4 RPT Device

FIG. 4A shows a RPT device in accordance with one form of the presenttechnology.

FIG. 4B shows a schematic diagram of the pneumatic path of a RPT devicein accordance with one form of the present technology. The directions ofupstream and downstream are indicated.

FIG. 4C shows a schematic diagram of the electrical components of a RPTdevice in accordance with one aspect of the present technology.

FIG. 4D shows a schematic diagram of the algorithms implemented in a RPTdevice in accordance with an aspect of the present technology. In thisfigure, arrows with solid lines indicate an actual flow of information,for example via an electronic signal.

FIG. 4E is a flow chart illustrating a method carried out by the therapyengine module of FIG. 4 d in accordance with one aspect of the presenttechnology.

4.5 Humidifier

FIG. 5A shows an isometric view of a humidifier in accordance with oneaspect of the present technology.

FIG. 5B shows an isometric view of a humidifier in accordance with oneaspect of the present technology, showing a humidifier reservoir 5110removed from the humidifier reservoir dock 5130.

FIG. 5C shows a schematic of a humidifier in accordance with one aspectof the present technology.

4.6 Breathing Waveforms

FIG. 6A shows a model typical breath waveform of a person whilesleeping.

FIG. 6 b shows a patient during Non-REM sleep breathing normally over aperiod of about ninety seconds.

FIG. 6C shows polysomnography of a patient before treatment.

FIG. 6D shows patient flow data where the patient is experiencing aseries of total obstructive apneas.

FIG. 6E shows a scaled inspiratory portion of a breath where the patientis experiencing low frequency inspiratory snore.

4.7 Heat and Moisture Exchanger

FIG. 7A shows a cross sectional view of a HME 7000 comprising a singlelayer 7001 in accordance with one aspect of the present technology.

FIG. 7B shows examples of a single corrugation 7030 of a HME 7000 inaccordance with one aspect of the present technology.

FIG. 7C is a schematic diagram showing a HME 7000 comprising a pluralityof layers 7001 stacked along both a vertical and horizontal axis.

FIG. 7D is a diagram that illustrates a HME under preload to compressthe corrugations in a fixed volume such that the number of layers 7001is increased within the fixed volume.

FIG. 8A displays a corrugated structure 7002 comprising a plurality ofcorrugations 7030, wherein the corrugated structure is rolled to form aHME 7000.

FIG. 8B shows an example of a patient interface 3000 comprising a HME7000 positioned within the plenum chamber 3200 according to the presenttechnology.

FIG. 8C shows an example of a patient interface 3000 comprising a HME7000 positioned within the plenum chamber 3200 according to the presenttechnology.

FIG. 8D shows an example of a patient interface 3000 comprising a HME7000 positioned within the plenum chamber 3200 according to the presenttechnology.

FIG. 9A displays an exploded view of another patient interface 3000comprising a HME 7000 and housed within a vent adaptor 3410 according tothe present technology.

FIG. 9B displays an exploded view of another patient interface 3000comprising a HME 7000 and housed within a vent adaptor 3410 according tothe present technology.

FIG. 9C displays a top view of a further example of a patient interface3000 in accordance with the present technology.

FIG. 9D displays a perspective view of a further example of a patientinterface 3000 in accordance with the present technology.

FIG. 9E displays a posterior view of a further example of a patientinterface 3000 in accordance with the present technology.

FIG. 9F displays a side view of a further example of a patient interface3000 in accordance with the present technology.

FIG. 9G displays a bottom view of a further example of a patientinterface 3000 in accordance with the present technology.

FIG. 9H displays a bottom perspective view of a further example of apatient interface 3000 in accordance with the present technology.

FIG. 9I displays a bottom perspective view of a further example of apatient interface 3000 in accordance with the present technology.

FIG. 9J displays a cross sectional view of a further example of apatient interface 3000 taken through line 9J-9J of FIG. 9 in accordancewith the present technology.

FIG. 10A shows an anterior view of the HME frame 7003 of the removableHME 7000.

FIG. 10B shows a posterior view of the HME frame 7003 of the removableHME 7000.

FIG. 10C shows a side view of the HME frame 7003 of the removable HME7000.

FIG. 10D shows a bottom view of the HME frame 7003 of the removable HME7000.

FIG. 10E shows a first perspective of the HME frame 7003 of theremovable HME 7000.

FIG. 10F shows a second perspective of the HME frame 7003 of theremovable HME 7000.

FIG. 11A shows the removable HME 7000 of the further example wherein amagnified view of the layers 7001 is shown.

FIG. 11B shows an anterior view of the removable HME 7000.

FIG. 11C shows a posterior view of the removable HME 7000.

FIG. 11D shows a side view of the removable HME 7000.

FIG. 11E shows a bottom view of the removable HME 7000.

FIG. 11F shows a first perspective view of the removable HME 7000 ofFIG. 71 .

FIG. 11G shows a second perspective view of the removable HME 7000 ofFIG. 71 .

FIG. 12A shows an anterior perspective view of the HME housing portion3410 of the patient interface 3000.

FIG. 12B shows a posterior perspective view of the HME housing portion3410 of the patient interface 3000.

FIG. 12C shows a top perspective view of the HME housing portion 3410 ofthe patient interface 3000.

FIG. 12D shows a posterior view of the HME housing portion 3410 of thepatient interface 3000.

FIG. 13A shows a flow diagram of an exemplary process followed forselecting a suitable heat and moisture exchanger (HME or HMX).

FIG. 13B shows a chart of humidified lung weight loss with various typesof humidification.

FIG. 13C shows various examples of corrugations or flute configurationsforming the corrugated structure that may be utilised in an HMEaccording to examples of the present technology.

FIG. 13D shows the parameters of various exemplary corrugated structuresaccording to examples of the present technology.

FIG. 13E shows the measurements used to provide the parameters listed inthe chart of FIG. 13D.

FIG. 14A shows a rear view of a patient interface with a HME accordingto an example of the present technology.

FIG. 14B shows a front perspective view of a patient interface with aHME according to an example of the present technology.

FIG. 14C shows a front perspective view of a patient interface with aHME and a supporting membrane according to an example of the presenttechnology.

FIG. 14D shows a front view of a patient interface with a HME accordingto an example of the present technology.

FIG. 14E shows a front view of a patient interface with a HME and asupporting membrane according to an example of the present technology.

FIG. 14F shows a side view of a patient interface with a HME donned on apatient according to an example of the present technology.

FIG. 15A shows a side view of a patient interface with a HME donned on apatient according to an example of the present technology.

FIG. 15B shows a front view of a patient interface with a HME accordingto an example of the present technology.

FIG. 15C shows a rear view of a patient interface with a HME and asupporting membrane according to an example of the present technology.

FIG. 16 shows a rear view of a HME and a supporting membrane accordingto an example of the present technology.

FIG. 17 a graph comparing the humidity added above ambient humidity atdifferent therapeutic pressures and flow rates when a HME is placed in aknown mask (ResMed Quattro FX).

5 DETAILED DESCRIPTION OF EXAMPLES OF THE TECHNOLOGY

Before the present technology is described in further detail, it is tobe understood that the technology is not limited to the particularexamples described herein, which may vary. It is also to be understoodthat the terminology used in this disclosure is for the purpose ofdescribing only the particular examples discussed herein, and is notintended to be limiting.

The following description is provided in relation to various exampleswhich may share one or more common characteristics and/or features. Itis to be understood that one or more features of any one example may becombinable with one or more features of another example or otherexamples. In addition, any single feature or combination of features inany of the examples may constitute a further example.

5.1 Therapy

In one form, the present technology comprises a method for treating arespiratory disorder comprising the step of applying positive pressureto the entrance of the airways of a patient 1000.

In certain examples of the present technology, a supply of air atpositive pressure is provided to the nasal passages of the patient viaone or both nares.

In certain examples of the present technology, mouth breathing islimited, restricted or prevented.

5.2 Treatment Systems

In one form, the present technology comprises an apparatus or device fortreating a respiratory disorder. The apparatus or device may comprise aRPT device 4000 for supplying pressurised respiratory gas, such as air,to the patient 1000 via an air circuit 4170 to a patient interface 3000.

5.3 Patient Interface

A non-invasive patient interface 3000 in accordance with one aspect ofthe present technology comprises the following functional aspects: aseal-forming structure 3100, a plenum chamber 3200, a positioning andstabilising structure 3300 and one form of connection port 3600 forconnection to air circuit 4170. In some forms a functional aspect may beprovided by one or more physical components. In some forms, one physicalcomponent may provide one or more functional aspects. In use theseal-forming structure 3100 is arranged to surround an entrance to theairways of the patient so as to facilitate the supply of air at positivepressure to the airways.

5.3.1 Seal-Forming Structure

In one form of the present technology, a seal-forming structure 3100provides a seal-forming surface, and may additionally provide acushioning function.

A seal-forming structure 3100 in accordance with the present technologymay be constructed from a soft, flexible, resilient material such assilicone.

In one form, the seal-forming structure 3100 comprises a sealing flange3110 and a support flange 3120. The sealing flange 3110 may comprise arelatively thin member with a thickness of less than about 1 mm, forexample about 0.25 mm to about 0.45 mm, that extends around theperimeter 3210 of the plenum chamber 3200. Support flange 3120 may berelatively thicker than the sealing flange 3110. The support flange 3120is disposed between the sealing flange 3110 and the marginal edge 3220of the plenum chamber 3200, and extends at least part of the way aroundthe perimeter 3210. The support flange 3120 is or includes a spring-likeelement and functions to support the sealing flange 3110 from bucklingin use. In use the sealing flange 3110 can readily respond to systempressure in the plenum chamber 3200 acting on its underside to urge itinto tight sealing engagement with the face.

In one form the seal-forming portion of the non-invasive patientinterface 3000 comprises a pair of nasal puffs, or nasal pillows, eachnasal puff or nasal pillow being constructed and arranged to form a sealwith a respective naris of the nose of a patient.

Nasal pillows in accordance with an aspect of the present technologyinclude: a frusto-cone, at least a portion of which forms a seal on anunderside of the patient's nose; a stalk, a flexible region on theunderside of the frusto-cone and connecting the frusto-cone to thestalk. In addition, the structure to which the nasal pillow of thepresent technology is connected includes a flexible region adjacent thebase of the stalk. The flexible regions can act in concert to facilitatea universal joint structure that is accommodating of relativemovement—both displacement and angular—of the frusto-cone and thestructure to which the nasal pillow is connected. For example, thefrusto-cone may be axially displaced towards the structure to which thestalk is connected.

In one form the non-invasive patient interface 3000 comprises aseal-forming portion that forms a seal in use on an upper lip region(that is, the lip superior) of the patient's face.

In one form the non-invasive patient interface 3000 comprises aseal-forming portion that forms a seal in use on a chin-region of thepatient's face.

5.3.2 Plenum Chamber

The plenum chamber 3200 may have a perimeter 3210 that is shaped to becomplementary to the surface contour of the face of an average person inthe region where a seal will form in use. In use, a marginal edge 3220of the plenum chamber 3200 is positioned in close proximity to anadjacent surface of the face. Actual contact with the face is providedby the seal-forming structure 3100. The seal-forming structure 3100extends in use about the entire perimeter 3210 of the plenum chamber3200.

5.3.3 Positioning and Stabilising Structure

The seal-forming portion 3100 of the patient interface 3000 of thepresent technology is held in sealing position in use by the positioningand stabilising structure 3300.

5.3.4 Vent

In one form, the patient interface 3000 includes a vent 3400 constructedand arranged to allow for the washout of exhaled carbon dioxide.

One form of vent 3400 in accordance with the present technologycomprises a plurality of holes, for example, about 20 to about 80 holes,or about 40 to about 60 holes, or about 45 to about 55 holes.

The vent 3400 is located in the plenum chamber 3200. Alternatively, thevent 3400 is located in a decoupling structure 3500, e.g. a swivel 3510.

5.3.5 Decoupling Structure(s)

In one form the patient interface 3000 includes at least one decouplingstructure 3500, for example a swivel 3510 or a ball and socket 3520.

5.3.6 Connection Port

Connection port 3600 allows for connection to the air circuit 4170.

5.3.7 Forehead Support

In one form, the patient interface 3000 includes a forehead support3700.

5.3.8 Anti-Asphyxia Valve

In one form, the patient interface 3000 includes an anti-asphyxia valve3800.

5.3.9 Ports

In one form of the present technology, a patient interface 3000 includesone or more ports, that allow access to the volume within the plenumchamber 3200. In one form this allows a clinician to supply supplementaloxygen. In one form this allows for the direct measurement of a propertyof gases within the plenum chamber 3200, such as the pressure.

5.4 RPT Device

A RPT device 4000 in accordance with one aspect of the presenttechnology comprises mechanical and pneumatic components 4100,electrical components 4200 and is configured to execute one or morealgorithms 4300. The RPT device may have an external housing 4010, whichmay be formed in two parts, an upper portion 4012 and a lower portion4014. Furthermore, the external housing 4010 may include one or morepanel(s) 4015. The RPT device 4000 comprises a chassis 4016 thatsupports one or more internal components of the RPT device 4000. The RTdevice 4000 may include a handle 4018.

The pneumatic path of the RPT device 4000 may comprise one or more airpath items, e.g. an inlet air filter 4112, an inlet muffler 4122, apressure generator 4140 capable of supplying air at positive pressure(e.g., a blower 4142), an outlet muffler 4124 and one or moretransducers 4270, such as pressure sensors 4272 and flow sensors 4274

One or more of the air path items may be located within a removableunitary structure which will be referred to as a pneumatic block 4020.The pneumatic block 4020 may be located within the external housing4010. In one form a pneumatic block 4020 is supported by, or formed aspart of the chassis 4016.

The RPT device 4000 may include an electrical power supply 4210, one ormore input devices 4220, a central controller 4230, a therapy devicecontroller 4240, a pressure generator 4140, one or more protectioncircuits 4250, memory 4260, transducers 4270, data communicationinterface 4280 and one or more output devices 4290. Electricalcomponents 4200 may be mounted on a single Printed Circuit BoardAssembly (PCBA) 4202. In an alternative form, the RPT device 4000 mayinclude more than one PCBA 4202.

5.4.1 RPT Device Mechanical & Pneumatic Components

An RPT device may comprise one or more of the following components in anintegral unit. In an alternative form, one or more of the followingcomponents may be located as respective separate units.

5.4.1.1 Air Filter(s)

A RPT device in accordance with one form of the present technology mayinclude an air filter 4110, or a plurality of air filters 4110.

In one form, an inlet air filter 4112 is located at the beginning of thepneumatic path upstream of a pressure generator 4140. See FIG. 4B.

In one form, an outlet air filter 4114, for example an antibacterialfilter, is located between an outlet of the pneumatic block 4020 and apatient interface 3000. See FIG. 4B.

5.4.1.2 Muffler(s)

In one form of the present technology, an inlet muffler 4122 is locatedin the pneumatic path upstream of a pressure generator 4140. See FIG.4B.

In one form of the present technology, an outlet muffler 4124 is locatedin the pneumatic path between the pressure generator 4140 and a patientinterface 3000. See FIG. 4B.

5.4.1.3 Pressure Generator

In one form of the present technology, a pressure generator 4140 forproducing a flow, or a supply, of air at positive pressure is acontrollable blower 4142. For example the blower 4142 may include abrushless DC motor 4144 with one or more impellers housed in a volute.The blower may be capable of delivering a supply of air, for example ata rate of up to about 120 litres/minute, at a positive pressure in arange from about 4 cmH₂O to about 20 cmH₂O, or in other forms up toabout 30 cmH₂O. The blower may be as described in any one of thefollowing patents or patent applications the contents of which areincorporated herein in their entirety: U.S. Pat. Nos. 7,866,944;8,638,014; 8,636,479; and PCT patent application publication number WO2013/020167.

The pressure generator 4140 is under the control of the therapy devicecontroller 4240.

In other forms, a pressure generator 4140 may be a piston-driven pump, apressure regulator connected to a high pressure source (e.g. compressedair reservoir), or a bellows.

5.4.1.4 Transducer(s)

Transducers may be internal of the RPT device, or external of the RPTdevice. External transducers may be located for example on or form partof the air circuit, e.g. the patient interface. External transducers maybe in the form of non-contact sensors such as a Doppler radar movementsensor that transmit or transfer data to the RPT device.

In one form of the present technology, one or more transducers 4270 arelocated upstream and/or downstream of the pressure generator 4140. Theone or more transducers 4270 may be constructed and arranged to measureproperties such as a flow rate, a pressure or a temperature at thatpoint in the pneumatic path.

In one form of the present technology, one or more transducers 4270 maybe located proximate to the patient interface 3000.

In one form, a signal from a transducer 4270 may be filtered, such as bylow-pass, high-pass or band-pass filtering.

5.4.1.4.1 Flow Transducer

A flow transducer 4274 in accordance with the present technology may bebased on a differential pressure transducer, for example, an SDP600Series differential pressure transducer from SENSIRION.

In one form, a signal representing a flow rate such as a total flow Qtfrom the flow transducer 4274 is received by the central controller4230.

5.4.1.4.2 Pressure Transducer

A pressure transducer 4272 in accordance with the present technology islocated in fluid communication with the pneumatic path. An example of asuitable pressure transducer is a sensor from the HONEYWELL ASDX series.An alternative suitable pressure transducer is a sensor from the NPASeries from GENERAL ELECTRIC.

In one form, a signal from the pressure transducer 4272 is received bythe central controller 4230.

5.4.1.4.3 Motor Speed Transducer

In one form of the present technology a motor speed transducer 4276 isused to determine a rotational velocity of the motor 4144 and/or theblower 4142. A motor speed signal from the motor speed transducer 4276may be provided to the therapy device controller 4240. The motor speedtransducer 4276 may, for example, be a speed sensor, such as a Halleffect sensor.

5.4.1.5 Anti-Spill Back Valve

In one form of the present technology, an anti-spill back valve islocated between the humidifier 5000 and the pneumatic block 4020. Theanti-spill back valve is constructed and arranged to reduce the riskthat water will flow upstream from the humidifier 5000, for example tothe motor 4144.

5.4.1.6 Air Circuit

An air circuit 4170 in accordance with an aspect of the presenttechnology is a conduit or a tube constructed and arranged in use toallow a flow of air to travel between two components such as thepneumatic block 4020 and the patient interface 3000.

In particular, the air circuit 4170 may be in fluid connection with theoutlet of the pneumatic block and the patient interface. The air circuitmay be referred to as an air delivery tube. In some cases there may beseparate limbs of the circuit for inhalation and exhalation. In othercases a single limb is used.

5.4.1.7 Oxygen Delivery

In one form of the present technology, supplemental oxygen 4180 isdelivered to one or more points in the pneumatic path, such as upstreamof the pneumatic block 4020, to the air circuit 4170 and/or to thepatient interface 3000.

5.4.2 RPT Device Electrical Components

5.4.2.1 Power Supply

A power supply 4210 may be located internal or external of the externalhousing 4010 of the RPT device 4000.

In one form of the present technology power supply 4210 provideselectrical power to the RPT device 4000 only. In another form of thepresent technology, power supply 4210 provides electrical power to bothRPT device 4000 and humidifier 5000.

5.4.2.2 Input Devices

In one form of the present technology, a RPT device 4000 includes one ormore input devices 4220 in the form of buttons, switches or dials toallow a person to interact with the device. The buttons, switches ordials may be physical devices, or software devices accessible via atouch screen. The buttons, switches or dials may, in one form, bephysically connected to the external housing 4010, or may, in anotherform, be in wireless communication with a receiver that is in electricalconnection to the central controller 4230.

In one form the input device 4220 may be constructed and arranged toallow a person to select a value and/or a menu option.

5.4.2.3 Central Controller

In one form of the present technology, the central controller 4230 isone or a plurality of processors suitable to control a RPT device 4000.

Suitable processors may include an x86 INTEL processor, a processorbased on ARM Cortex-M processor from ARM Holdings such as an STM32series microcontroller from ST MICROELECTRONIC. In certain alternativeforms of the present technology, a 32-bit RISC CPU, such as an STR9series microcontroller from ST MICROELECTRONICS or a 16-bit RISC CPUsuch as a processor from the MSP430 family of microcontrollers,manufactured by TEXAS INSTRUMENTS may also be suitable.

In one form of the present technology, the central controller 4230 is adedicated electronic circuit.

In one form, the central controller 4230 is an application-specificintegrated circuit. In another form, the central controller 4230comprises discrete electronic components.

The central controller 4230 may be configured to receive input signal(s)from one or more transducers 4270, and one or more input devices 4220.

The central controller 4230 may be configured to provide outputsignal(s) to one or more of an output device 4290, a therapy devicecontroller 4240, a data communication interface 4280 and humidifiercontroller 5250.

In some forms of the present technology, the central controller 4230 isconfigured to implement the one or more methodologies described herein,such as the one or more algorithms 4300 expressed as computer programsstored in a non-transitory computer readable storage medium, such asmemory 4260. In some forms of the present technology, the centralcontroller 4230 may be integrated with a RPT device 4000. However, insome forms of the present technology, some methodologies may beperformed by a remotely located device. For example, the remotelylocated device may determine control settings for a ventilator or detectrespiratory related events by analysis of stored data such as from anyof the sensors described herein.

5.4.2.4 Clock

The RPT device 4000 may include a clock 4232 that is connected to thecentral controller 4230.

5.4.2.5 Therapy Device Controller

In one form of the present technology, therapy device controller 4240 isa control module 4330 that forms part of the algorithms 4300 executed bythe central controller 4230.

In one form of the present technology, therapy device controller 4240 isa dedicated motor control integrated circuit. For example, in one form aMC33035 brushless DC motor controller, manufactured by ONSEMI is used.

5.4.2.6 Protection Circuits

The one or more protection circuits 4250 in accordance with the presenttechnology may comprise an electrical protection circuit, a temperatureand/or pressure safety circuit.

5.4.2.7 Memory

In accordance with one form of the present technology the RPT device4000 includes memory 4260, e.g., non-volatile memory. In some forms,memory 4260 may include battery powered static RAM. In some forms,memory 4260 may include volatile RAM.

The memory 4260 may be located on the PCBA 4202. Memory 4260 may be inthe form of EEPROM, or NAND flash.

Additionally or alternatively, RPT device 4000 includes a removable formof memory 4260, for example a memory card made in accordance with theSecure Digital (SD) standard.

In one form of the present technology, the memory 4260 acts as anon-transitory computer readable storage medium on which are storedcomputer program instructions expressing the one or more methodologiesdescribed herein, such as the one or more algorithms 4300.

5.4.2.8 Data Communication Systems

In one form of the present technology, a data communication interface4280 is provided, and is connected to the central controller 4230. Datacommunication interface 4280 may be connectable to remote externalcommunication network 4282 and/or a local external communication network4284. A remote external communication network 4282 may be connectable toremote external device 4286. A local external communication network 4284may be connectable to local external device 4288.

In one form, data communication interface 4280 is part of the centralcontroller 4230. In another form, data communication interface 4280 isseparate from the central controller 4230, and may comprise anintegrated circuit or a processor.

In one form, remote external communication network 4282 is the Internet.The data communication interface 4280 may use wired communication (e.g.via Ethernet, or optical fibre) or a wireless protocol (e.g. CDMA, GSM,LTE) to connect to the Internet.

In one form, local external communication network 4284 utilises one ormore communication standards, such as Bluetooth, or a consumer infraredprotocol.

In one form, remote external device 4286 is one or more computers, forexample a cluster of networked computers. In one form, remote externaldevice 4286 may be virtual computers, rather than physical computers. Ineither case, such remote external device 4286 may be accessible to anappropriately authorised person such as a clinician.

A local external device 4288 may be a personal computer, mobile phone,tablet or remote control.

5.4.2.9 Output Devices Including Optional Display, Alarms

An output device 4290 in accordance with the present technology may takethe form of one or more of a visual, audio and haptic unit. A visualdisplay may be a Liquid Crystal Display (LCD) or Light Emitting Diode(LED) display.

5.4.2.9.1 Display Driver

A display driver 4292 receives as an input the characters, symbols, orimages intended for display on the display 4294, and converts them tocommands that cause the display 4294 to display those characters,symbols, or images.

5.4.2.9.2 Display

A display 4294 is configured to visually display characters, symbols, orimages in response to commands received from the display driver 4292.For example, the display 4294 may be an eight-segment display, in whichcase the display driver 4292 converts each character or symbol, such asthe figure “0”, to eight logical signals indicating whether the eightrespective segments are to be activated to display a particularcharacter or symbol.

5.4.3 RPT Device Algorithms

5.4.3.1 Pre-Processing Module

A pre-processing module 4310 in accordance with one form of the presenttechnology receives as an input a signal from a transducer 4270, forexample a flow transducer 4274 or pressure transducer 4272, and performsone or more process steps to calculate one or more output values thatwill be used as an input to another module, for example a therapy enginemodule 4320.

In one form of the present technology, the output values include theinterface or mask pressure Pm, the respiratory flow Qr, and theunintentional leak flow Ql.

In various forms of the present technology, the pre-processing module4310 comprises one or more of the following algorithms: pressurecompensation 4312, vent flow 4314 (e.g. intentional leak), leak flow4316 (e.g. unintentional leak), and respiratory flow 4318.

5.4.3.1.1 Pressure Compensation

In one form of the present technology, a pressure compensation algorithm4312 receives as an input a signal indicative of the pressure in thepneumatic path proximal to an outlet of the pneumatic block. Thepressure compensation algorithm 4312 estimates the pressure drop throughthe air circuit 4170 and provides as an output an estimated pressure,Pm, in the patient interface 3000.

5.4.3.1.2 Vent Flow

In one form of the present technology, a vent flow calculation algorithm4314 receives as an input an estimated pressure, Pm, in the patientinterface 3000 and estimates a vent flow of air, Qv, from a vent 3400 ina patient interface 3000.

5.4.3.1.3 Leak Flow

In one form of the present technology, a leak flow algorithm 4316receives as an input a total flow, Qt, and a vent flow Qv, and providesas an output an estimate of the unintentional leak, i.e. leak flow, Ql,by calculating an average of the difference between total flow Qt andvent flow Qv over a period sufficiently long to include severalbreathing cycles, e.g. about 10 seconds.

In one form, the leak flow algorithm 4316 receives as an input a totalflow Qt, a vent flow Qv, and an estimated pressure, Pm, in the patientinterface 3000, and provides as an output a leak flow Ql, by calculatinga leak conductance, and determining a leak flow Ql to be a function ofleak conductance and pressure, Pm. Leak conductance may be calculated asthe quotient of low pass filtered non-vent flow equal to the differencebetween total flow Qt and vent flow Qv, and low pass filtered squareroot of pressure Pm, where the low pass filter time constant has a valuesufficiently long to include several breathing cycles, e.g. about 10seconds.

5.4.3.1.4 Respiratory Flow

In one form of the present technology, a respiratory flow algorithm 4318receives as an input a total flow, Qt, a vent flow, Qv, and a leak flow,Ql, and estimates a respiratory flow of air, Qr, to the patient, bysubtracting the vent flow Qv and the leak flow Ql from the total flowQt.

5.4.3.2 Therapy Engine Module

In one form of the present technology, a therapy engine module 4320receives as inputs one or more of a pressure, Pm, in a patient interface3000, and a respiratory flow of air to a patient, Qr, and provides as anoutput, one or more therapy parameters.

In one form of the present technology, a therapy parameter is a CPAPtreatment pressure Pt.

In one form of the present technology, therapy parameters are one ormore of a level of pressure support, and a target ventilation.

In various forms, the therapy engine module 4320 comprises one or moreof the following algorithms: phase determination 4321, waveformdetermination 4322, ventilation determination 4323, inspiratory flowlimitation determination 4324, apnea/hypopnea determination 4325, snoredetermination 4326, airway patency determination 4327, and therapyparameter determination 4328.

5.4.3.2.1 Phase Determination

In one form of the present technology, the RPT device 4000 does notdetermine phase.

In one form of the present technology, a phase determination algorithm4321 receives as an input a signal indicative of respiratory flow, Qr,and provides as an output a phase Φ of a breathing cycle of a patient1000.

In one form, the phase output is a discrete variable with values ofeither inhalation or exhalation. In one implementation of this form, thephase Φ is determined to have a discrete value of inhalation when arespiratory flow Qr has a positive value that exceeds a positivethreshold, and the phase Φ is determined to have a discrete value ofexhalation when a respiratory flow Qr has a value that is more negativethan a negative threshold. By convention in this implementation, thephase value during inhalation may be set to 0, while the phase valueduring inhalation may be set to 1.

In one form, the phase output is a discrete variable with values of oneof inhalation, mid-inspiratory pause, and exhalation.

In one form, the phase output is a continuous variable, for examplevarying from 0 to 1, or 0 to 2π radians.

5.4.3.2.2 Waveform Determination

In one form of the present technology, the therapy engine module 4320provides an approximately constant treatment pressure throughout arespiratory cycle of a patient.

In one form of the present technology, the therapy engine module 4320provides a treatment pressure that varies over the respiratory cycleaccording to a waveform of pressure vs phase.

In one form of the present technology, a waveform determinationalgorithm 4322 provides as an output the pressure-phase waveform P(Φ).The pressure-phase waveform P(Φ) may be valued between 0 and 1.

The predetermined waveform P(Φ) may be provided as a lookup table ofvalues P as a function of phase values Φ. The predetermined waveformP(Φ) may alternatively be provided as one or more parameters thatcharacterise the waveform P(Φ) according to a predetermined parametricdescription.

In one form, the waveform is maintained at an approximately constantlevel for all values of phase.

In one form, the waveform is a square wave, having a constant highervalue for some values of phase, and a constant lower level for othervalues of phase. In this form, the returned parameter may be a thresholdvalue of phase above which the waveform rises from the lower level tothe higher level.

In one form, the waveform P(Φ) has two exponential portions, anexponential rise according to one time constant for values of phase upto a threshold, and an exponential decay for values of phase above thethreshold. In this form, the returned parameters may be the two timeconstants and the threshold.

5.4.3.2.3 Ventilation Determination

In one form of the present technology, a ventilation determinationalgorithm 4323 receives an input a respiratory flow Qr, and determines ameasure indicative of patient ventilation, Vent.

In one form ventilation determination algorithm 4323 determines acurrent value of patient ventilation, Vent, as half the low-passfiltered absolute value of respiratory flow, Qr.

5.4.3.2.4 Determination of Inspiratory Flow Limitation

In one form of the present technology, the central controller 4230executes one or more algorithms 4324 for the detection of inspiratoryflow limitation.

In one form the algorithm 4324 receives as an input a respiratory flowsignal Qr and provides as an output a metric of the extent to which theinspiratory portion of the breath exhibits inspiratory flow limitation.

In one form of the present technology, the inspiratory portion of eachbreath is identified by a zero-crossing detector. A number of evenlyspaced points (for example, sixty-five), representing points in time,are interpolated by an interpolator along the inspiratory flow-timecurve for each breath. The curve described by the points is then scaledby a scaler to have unity length (duration/period) and unity area toremove the effects of changing respiratory rate and depth. The scaledbreaths are then compared in a comparator with a pre-stored templaterepresenting a normal unobstructed breath, similar to the inspiratoryportion of the breath shown in FIG. 6A. Breaths deviating by more than aspecified threshold (typically 1 scaled unit) at any time during theinspiration from this template, such as those due to coughs, sighs,swallows and hiccups, as determined by a test element, are rejected. Fornon-rejected data, a moving average of the first such scaled point iscalculated by the central controller 4230 for the preceding severalinspiratory events. This is repeated over the same inspiratory eventsfor the second such point, and so on. Thus, for example, sixty fivescaled data points are generated by the central controller 4230, andrepresent a moving average of the preceding several inspiratory events,e.g. three events. The moving average of continuously updated values ofthe (e.g. sixty five) points are hereinafter called the “scaled flow”,designated as Qs(t). Alternatively, a single inspiratory event can beutilised rather than a moving average.

From the scaled flow, two shape factors relating to the determination ofpartial obstruction may be calculated.

Shape factor 1 is the ratio of the mean of the middle (e.g. thirty-two)scaled flow points to the mean overall (e.g. sixty-five) scaled flowpoints. Where this ratio is in excess of unity, the breath will be takento be normal. Where the ratio is unity or less, the breath will be takento be obstructed. A ratio of about 1.17 is taken as a threshold betweenpartially obstructed and unobstructed breathing, and equates to a degreeof obstruction that would permit maintenance of adequate oxygenation ina typical user.

Shape factor 2 is calculated as the RMS deviation from unit scaled flow,taken over the middle (e.g. thirty two) points. An RMS deviation ofabout 0.2 units is taken to be normal. An RMS deviation of zero is takento be a totally flow-limited breath. The closer the RMS deviation tozero, the breath will be taken to be more flow limited.

Shape factors 1 and 2 may be used as alternatives, or in combination. Inother forms of the present technology, the number of sampled points,breaths and middle points may differ from those described above.Furthermore, the threshold values can other than those described.

5.4.3.2.5 Determination of Apneas and Hypopneas

In one form of the present technology, the central controller 4230executes one or more algorithms 4325 for the determination of thepresence of apneas and/or hypopneas.

The one or more algorithms 4325 may receive as an input a respiratoryflow signal Qr and provide as an output a flag that indicates that anapnea or a hypopnea has been detected.

In one form, an apnea will be said to have been detected when a functionof respiratory flow Qr falls below a flow threshold for a predeterminedperiod of time. The function may determine a peak flow, a relativelyshort-term mean flow, or a flow intermediate of relatively short-termmean and peak flow, for example an RMS flow. The flow threshold may be arelatively long-term measure of flow.

In one form, a hypopnea will be said to have been detected when afunction of respiratory flow Qr falls below a second flow threshold fora predetermined period of time. The function may determine a peak flow,a relatively short-term mean flow, or a flow intermediate of relativelyshort-term mean and peak flow, for example an RMS flow. The second flowthreshold may be a relatively long-term measure of flow. The second flowthreshold is greater than the flow threshold used to detect apneas.

5.4.3.2.6 Determination of Snore

In one form of the present technology, the central controller 4230executes one or more snore algorithms 4326 for the detection of snore.

In one form the snore algorithm 4326 receives as an input a respiratoryflow signal Qr and provides as an output a metric of the extent to whichsnoring is present.

The algorithm 4326 may comprise the step of determining the intensity ofthe flow signal in the range of 30-300 Hz. Further, algorithm 4326 maycomprise a step of filtering the respiratory flow signal Qr to reducebackground noise, e.g. the sound of airflow in the system from theblower.

5.4.3.2.7 Determination of Airway Patency

In one form of the present technology, the central controller 4230executes one or more algorithms 4327 for the determination of airwaypatency.

In one form, airway patency algorithm 4327 receives as an input arespiratory flow signal Qr, and determines the power of the signal inthe frequency range of about 0.75 Hz and about 3 Hz. The presence of apeak in this frequency range is taken to indicate an open airway. Theabsence of a peak is taken to be an indication of a closed airway.

In one form, the frequency range within which the peak is sought is thefrequency of a small forced oscillation in the treatment pressure Pt. Inone implementation, the forced oscillation is of frequency 2 Hz withamplitude about 1 cmH₂O.

In one form, airway patency algorithm 4327 receives as an input arespiratory flow signal Qr, and determines the presence or absence of acardiogenic signal. The absence of a cardiogenic signal is taken to bean indication of a closed airway.

5.4.3.2.8 Determination of Therapy Parameters

In one form of the present technology, the central controller 4230executes one or more algorithms 4328 for the determination of one ormore therapy parameters using the values returned by one or more of theother algorithms in the therapy engine module 4320.

In one form of the present technology, the therapy parameter is aninstantaneous treatment pressure Pt. In one implementation of this form,the treatment pressure Pt is given byPt=AP(Φ)+P ₀  (1)

where:

-   -   A is the pressure support,    -   P(Φ) is the pressure-phase waveform value (in the range 0 to 1)        at the current value Φ of phase, and    -   P₀ is a base pressure.

Various therapy modes may be defined depending on the values of theparameters A and P₀. In some implementations of this form of the presenttechnology, the pressure support A is identically zero, so the treatmentpressure Pt is identically equal to the base pressure P₀ throughout therespiratory cycle. Such implementations are generally grouped under theheading of CPAP therapy.

The base pressure P₀ may be a constant value that is prescribed and/ormanually entered to the PAP device 4000. This alternative is sometimesreferred to as constant CPAP therapy. Alternatively, the base pressureP₀ may be continuously computed as a function of indices or measures ofone or more of sleep disordered breathing events such as flowlimitation, apnea, hypopnea, patency, and snore returned by therespective algorithms in the therapy engine module 4320. Thisalternative is sometimes referred to as APAP therapy.

In other implementations of this form, referred to as positive-pressureventilation, the pressure support A is non-zero. In some suchimplementations, in which the RPT device 4000 acts as aservo-ventilator, the therapy parameter determination algorithm 4328takes as input the current measure Vent of ventilation and a targetventilation value Vtgt and calculates a value of pressure support A tobring the current measure Vent of ventilation towards the target valueVtgt of ventilation. In such implementations, the pressure-phasewaveform P (Φ) is configured so as to attain a higher value during theinspiration portion of the respiratory cycle, and a lower value duringthe expiration portion of the respiratory cycle.

In such implementations, the therapy parameter determination algorithm4328 may apply a continuous control methodology to compute the pressuresupport A. One such continuous control methodology isProportional-Integral (PI) control, according to which the pressuresupport is computed as:A=G∫(Vent−Vtgt)dt  (2)

where G is the gain of the PI control.

Other continuous control methodologies that may be applied by thetherapy parameter determination algorithm 4328 include proportional (P),proportional-differential (PD), and proportional-integral-differential(PID).

Other control methodologies, referred to as discrete controlmethodologies, return a pressure support A that is one of a discrete setof predetermined values.

FIG. 4E is a flow chart illustrating a method 4500 carried out by thecentral controller 4230 as one implementation of the algorithm 4328. Themethod 4500 starts at step 4520, at which the central controller 4230compares the measure of the presence of apnea/hypopnea with a firstthreshold, and determines whether the measure of the presence ofapnea/hypopnea has exceeded the first threshold for a predeterminedperiod of time, indicating an apnea/hypopnea is occurring. If so, themethod 4500 proceeds to step 4540; otherwise, the method 4500 proceedsto step 4530. At step 4540, the central controller 4230 compares themeasure of airway patency with a second threshold. If the measure ofairway patency exceeds the second threshold, indicating the airway ispatent, the detected apnea/hypopnea is deemed central, and the method4500 proceeds to step 4560; otherwise, the apnea/hypopnea is deemedobstructive, and the method 4500 proceeds to step 4550.

At step 4530, the central controller 4230 compares the measure of flowlimitation with a third threshold. If the measure of flow limitationexceeds the third threshold, indicating inspiratory flow is limited, themethod 4500 proceeds to step 4550; otherwise, the method 4500 proceedsto step 4560.

At step 4550, the central controller 4230 increases the treatmentpressure Pt by a predetermined pressure increment ΔP, provided theincreased treatment pressure Pt would not exceed an upper limit Pmax. Inone implementation, the predetermined pressure increment ΔP and upperlimit Pmax are 1 cmH₂O and 20 cmH₂O respectively. The method 4500 thenreturns to step 4520.

At step 4560, the central controller 4230 decreases the treatmentpressure Pt by a decrement, provided the decreased treatment pressure Ptwould not fall below a lower limit Pmin. The method 4500 then returns tostep 4520. In one implementation, the decrement is proportional to thevalue of Pt−Pmin, so that the decrease in Pt to the lower limit Pmin inthe absence of any detected events is exponential. In oneimplementation, the constant of proportionality is set such that thetime constant τ of the exponential decrease of Pt is 60 minutes, and thelower limit Pmin is 4 cmH₂O. In other implementations, the time constantτ could be as low as 1 minute and as high as 300 minutes, or as low as 5minutes and as high as 180 minutes. Alternatively, the decrement in Ptcould be predetermined, so the decrease in Pt to the lower limit Pmin inthe absence of any detected events is linear.

5.4.3.3 Control Module

Therapy control module 4330 in accordance with one aspect of the presenttechnology receives as inputs the therapy parameters from the therapyengine module 4320, and controls the pressure generator 4140 to delivera flow of gas in accordance with the therapy parameters.

In one form of the present technology, the therapy parameter is atreatment pressure Pt, and the therapy control module 4330 controls thetherapy device 4245 to deliver a flow of gas whose mask pressure Pm atthe patient interface 3000 is equal to the treatment pressure Pt.

5.4.3.4 Detection of Fault Conditions

In one form of the present technology, the central controller 4230executes one or more methods for the detection of fault conditions. Thefault conditions detected by the one or more methods may include atleast one of the following:

-   -   Power failure (no power, or insufficient power)    -   Transducer fault detection    -   Failure to detect the presence of a component    -   Operating parameters outside recommended ranges (e.g. pressure,        flow, temperature, PaO₂)    -   Failure of a test alarm to generate a detectable alarm signal.

Upon detection of the fault condition, the corresponding algorithmsignals the presence of the fault by one or more of the following:

-   -   Initiation of an audible, visual &or kinetic (e.g. vibrating)        alarm    -   Sending a message to an external device    -   Logging of the incident

5.5 Humidifier

5.5.1 Humidifier Overview

In one form of the present technology there is provided a humidifier5000 (e.g. as shown in FIG. 5A) to change the absolute humidity of airor gas for delivery to a patient relative to ambient air. Typically, thehumidifier 5000 is used to increase the absolute humidity and increasethe temperature of the flow of air (relative to ambient air) beforedelivery to the patient's airways.

The humidifier 5000 may comprise a humidifier reservoir 5110, ahumidifier inlet 5002 to receive a flow of air, and a humidifier outlet5004 to deliver a humidified flow of air. In some forms, as shown inFIG. 5A and FIG. 5B, an inlet and an outlet of the humidifier reservoir5110 may be the humidifier inlet 5002 and the humidifier outlet 5004respectively. The humidifier 5000 may further comprise a humidifier base5006, which may be adapted to receive the humidifier reservoir 5110 andcomprise a heating element 5240.

5.5.2 Humidifier Mechanical Components

5.5.2.1 Water Reservoir

According to one arrangement, the humidifier 5000 may comprise a waterreservoir 5110 configured to hold, or retain, a volume of liquid (e.g.water) to be used for humidification of the flow of air. The waterreservoir 5110 is configured to hold a predetermined maximum volume ofwater in order to provide adequate humidification for at least theduration of respiratory therapy, such as one evening of sleep.Typically, the reservoir 5110 is configured to hold several hundredmillilitres of water, e.g. 300 millilitres (ml), 325 ml, 350 ml or 400ml. In other forms, the humidifier 5000 may be configured to receive asupply of water from an external water source such as a building's watersupply system.

According to one aspect, the water reservoir 5110 is configured to addhumidity to a flow of air from the RPT device 4000 as the flow of airtravels therethrough. In one form, the water reservoir 5110 may beconfigured to encourage the flow of air to travel in a tortuous paththrough the reservoir 5110 while in contact with the volume of watertherein.

According to one form, the reservoir 5110 may be removable from thehumidifier 5000, for example in a lateral direction as shown in FIG. 5Aand FIG. 5B.

The reservoir 5110 may also be configured to discourage egress of liquidtherefrom, such as when the reservoir 5110 is displaced and/or rotatedfrom its normal, working orientation, such as through any aperturesand/or in between its sub-components. As the flow of air to behumidified by the humidifier 5000 is typically pressurised, thereservoir 5110 may also be configured to prevent losses in pneumaticpressure through leak and/or flow impedance.

5.5.2.2 Conductive Portion

According to one arrangement, the reservoir 5110 comprises a conductiveportion 5120 configured to allow efficient transfer of heat from theheating element 5240 to the volume of liquid in the reservoir 5110. Inone form, the conductive portion 5120 may be arranged as a plate,although other shapes may also be suitable. All or a part of theconductive portion 5120 may be made of a thermally conductive materialsuch as aluminium (e.g. approximately 2 mm thick, such as 1 mm, 1.5 mm,2.5 mm or 3 mm), another heat conducting metal or some plastics. In somecases, suitable heat conductivity may be achieved with less conductivematerials of suitable geometry.

5.5.2.3 Humidifier Reservoir Dock

In one form, the humidifier 5000 may comprise a humidifier reservoirdock 5130 (as shown in FIG. 5B) configured to receive the humidifierreservoir 5110. In some arrangements, the humidifier reservoir dock 5130may comprise a locking feature such as a locking lever 5135 configuredto retain the reservoir 5110 in the reservoir dock 5130.

5.5.2.4 Water Level Indicator

The humidifier reservoir 5110 may comprise a water level indicator 5150as shown in FIG. 5A-5B. In some forms, the water level indicator 5150may provide one or more indications to a user such as the patient 1000or a care giver regarding a quantity of the volume of water in thehumidifier reservoir 5110. The one or more indications provided by thewater level indicator 5150 may include an indication of a maximum,predetermined volume of water, any portions thereof, such as 25%, 50% or75% or volumes such as 200 ml, 300 ml or 400 ml.

5.5.3 Humidifier Electrical & Thermal Components

The humidifier 5000 may comprise a number of electrical and/or thermalcomponents such as those listed below.

5.5.3.1 Humidifier Transducer(s)

The humidifier 5000 may comprise one or more humidifier transducers(sensors) 5210 instead of, or in addition to, transducers 4270 describedabove. Humidifier transducers 5210 may include one or more of an airpressure sensor 5212, an air flow sensor 5214, a temperature sensor5216, or a humidity sensor 5218 as shown in FIG. 5C. A humidifiertransducer 5210 may produce one or more output signals which may becommunicated to a controller such as the central controller 4230 and/orthe humidifier controller 5250. In some forms, a humidifier transducermay be located externally to the humidifier 5000 (such as in the aircircuit 4170) while communicating the output signal to the controller.

5.5.3.1.1 Pressure Transducer

One or more pressure transducers 5212 may be provided to the humidifier5000 in addition to, or instead of, a pressure transducer 4272 providedin the RPT device 4000.

5.5.3.1.2 Flow Transducer

One or more flow transducers 5214 may be provided to the humidifier 5000in addition to, or instead of, a flow transducer 4274 provided in theRPT device 4000.

5.5.3.1.3 Temperature Transducer

The humidifier 5000 may comprise one or more temperature transducers5216. The one or more temperature transducers 5216 may be configured tomeasure one or more temperatures such as of the heating element 5240and/or of the flow of air downstream of the humidifier outlet 5004. Insome forms, the humidifier 5000 may further comprise a temperaturesensor 5216 to detect the temperature of the ambient air.

5.5.3.1.4 Humidity Transducer

In one form, the humidifier 5000 may comprise one or more humiditysensors 5218 to detect a humidity of a gas, such as the ambient air. Thehumidity sensor 5218 may be placed towards the humidifier outlet 5004 insome forms to measure a humidity of the gas delivered from thehumidifier 5000. The humidity sensor may be an absolute humidity sensoror a relative humidity sensor.

5.5.3.2 Heating Element

A heating element 5240 may be provided to the humidifier 5000 in somecases to provide a heat input to one or more of the volume of water inthe humidifier reservoir 5110 and/or to the flow of air. The heatingelement 5240 may comprise a heat generating component such as anelectrically resistive heating track. One suitable example of a heatingelement 5240 is a layered heating element such as one described in thePCT Patent Application Publication Number WO 2012/171072, the entiredocument of which is incorporated herewithin by reference.

In some forms, the heating element 5240 may be provided in thehumidifier base 5006 where heat may be provided to the humidifierreservoir 5110 primarily by conduction as shown in FIG. 5B.

5.5.3.3 Humidifier Controller

According to one arrangement of the present technology, a humidifier5000 may comprise a humidifier controller 5250 as shown in FIG. 5C. Inone form, the humidifier controller 5250 may be a part of the centralcontroller 4230. In another form, the humidifier controller 5250 may bea separate controller, which may be in communication with the centralcontroller 4230.

In one form, the humidifier controller 5250 may receive as inputsmeasures of characteristics (such as temperature, humidity, pressureand/or flow rate), for example of the flow of air, the water in thereservoir 5110 and/or the humidifier 5000. The humidifier controller5250 may also be configured to execute or implement humidifieralgorithms and/or deliver one or more output signals.

As shown in FIG. 5C, the humidifier controller may comprise one or morecontrollers, such as a central humidifier controller 5251, a heated aircircuit controller 5254 configured to control the temperature of aheated air circuit 4171 and/or a heating element controller 5252configured to control the temperature of a heating element 5240.

5.6 Breathing Waveforms

FIG. 6A shows a model typical breath waveform of a person whilesleeping. The horizontal axis is time, and the vertical axis isrespiratory flow. While the parameter values may vary, a typical breathmay have the following approximate values: tidal volume, Vt, 0.5 L,inhalation time, Ti, 1.6 s, peak inspiratory flow, Qpeak, 0.4 L/s,exhalation time, Te, 2.4 s, peak expiratory flow, Qpeak, −0.5 L/s. Thetotal duration of the breath, Tot, is about 4 s. The person typicallybreathes at a rate of about 15 breaths per minute (BPM), withVentilation, Vent, about 7.5 L/minute. A typical duty cycle, the ratioof Ti to Tot is about 40%.

FIG. 6B shows a patient during Non-REM sleep breathing normally over aperiod of about ninety seconds, with about 34 breaths, being treatedwith Automatic PAP, and the mask pressure being about 11 cmH₂O. The topchannel shows oximetry (SpO₂), the scale has a range of saturation from90 to 99% in the vertical direction. The patient maintained a saturationof about 95% throughout the period shown. The second channel showsquantitative respiratory airflow, and the scale ranges from −1 to +1 LPSin a vertical direction, and with inspiration positive. Thoracic andabdominal movement are shown in the third and fourth channels.

FIG. 6C shows polysomnography of a patient before treatment. There areeleven signal channels from top to bottom with a 6 minute horizontalspan. The top two channels are both EEG (electoencephalogram) fromdifferent scalp locations. Periodic spikes in the second EEG representcortical arousal and related activity. The third channel down issubmental EMG (electromyogram). Increasing activity around the time ofarousals represents genioglossus recruitment. The fourth & fifthchannels are EOG (electro-oculogram). The sixth channel is anelectocardiogram. The seventh channel shows pulse oximetry (SpO₂) withrepetitive desaturations to below 70% from about 90%. The eighth channelis respiratory airflow using nasal cannula connected to a differentialpressure transducer. Repetitive apneas of 25 to 35 seconds alternatewith 10 to 15 second bursts of recovery breathing coinciding with EEGarousal and increased EMG activity. The ninth channel shows movement ofchest and the tenth shows movement of abdomen. The abdomen shows acrescendo of movement over the length of the apnea leading to thearousal. Both become untidy during the arousal due to gross bodymovement during recovery hyperpnea. The apneas are thereforeobstructive, and the condition is severe. The lowest channel is posture,and in this example it does not show change.

FIG. 6D shows patient flow data where the patient is experiencing aseries of total obstructive apneas. The duration of the recording isapproximately 160 seconds. Flow ranges from about +1 L/s to about −1.5L/s. Each apnea lasts approximately 10-15 s.

5.7 Heat and Moisture Exchanger (HME)

5.7.1 HME Overview

FIGS. 7A to 7D show examples of a HME according to the presenttechnology. FIG. 7A shows a cross section of a HME 7000 comprising acorrugated structure 7002 comprising a plurality of corrugations 7030between a substantially planar substrate top structure 7010 and asubstantially planar substrate base structure 7020 to form a concertinalayer 7001. The layer 7001 comprises a plurality of superior channels7012 formed between a superior surface of the corrugated structure 7002and the top structure 7010. In addition, the layer 7001 comprises aplurality of inferior channels 7022 between an inferior surface of thecorrugated structure 7002 and the base structure 7020. The HME 7000allows for a flow of breathable gas and expiratory gas to flow throughthe plurality of superior 7012 and inferior 7022 channels along asurface of the corrugated structure to exchange heat and moisture.Moisture is absorbed from the expiratory gas exhaled from a patient andretained in the material of the corrugated structure 7002. The materialof the corrugations 7030, the top structure 7010, and/or the basestructure 7020 may comprise paper or a paper based material that is ableto absorb water and/or heat. The material of the corrugations 7030, thetop structure 7010, and/or the base structure 7020 may be porous,water-permeable, and/or air-permeable. The retained moisture maysubsequently be redelivered to the patient by humidifying a flow ofbreathable gas delivered to the patient's airways. In other words, theflow of breathable gas delivered to the patient's airways may absorbmoisture from the HME 7000. FIG. 7B depicts the various dimensions of aHME according to these examples. A thickness of the top structure 7010and/or the base structure 7020 may be between 0.03-0.12 mm.

The plurality of corrugations 7030 increase the surface area of thecorrugated structure 7002 that allows for an increase in active surfacearea for the exchange of heat and moisture occurring between thecorrugated structure 7002 and the surrounding volume provided by theplurality of superior 7012 and inferior 7022 channels. The top structure7010 and the base structure 7020 may also be formed from the same heatand moisture exchanging material as the corrugated structure 7030.Alternatively, the top structure 7010 and/or the base structure 7020 maybe formed of a rigid or semi-rigid material that does not absorbmoisture to support the corrugated structure 7002.

The humidification performance of the HME 7000 is dependent on theeffective surface area of the HME 7000 provided in a fixed volume ofspace. The effective surface area is the surface area of the HME 7000that is exposed to the flow of breathable gas flowing along the surfaceof the HME where heat and moisture exchange occurs. The surface area perunit volume of the HME 7000 can be adjusted by providing corrugations7030 within the heat and moisture exchange portion of the HME 7000.Furthermore, the surface area per unit volume may also be adjusted bymodifying at least one of the fin thickness, pitch or height of thecorrugations or flutes, which have an impact on the surface area perunit volume of the HME 7000.

The HME 7000 may comprise a plurality of layers 7001 stacked along avertical axis of the HME 7000, as shown in FIG. 7C. The layers 7001 maybe vertically stacked such that the base structure 7020 is stacked ontop of the corrugated structure 7002 of an underlying adjacent layer7001. There may be also several layers 7001 of HME stacked in thehorizontal direction. Having a number of layers 7001 comprisingcorrugated structures 7002 that are stacked along a vertical axis of theHME 7000 further increases the surface area per unit volume of the HME.This increased surface area within a predefined volume allows forincreased efficiency in heat and moisture exchange of the HME 7000.Furthermore, the layers 7001 may be compressed under a preload, asdepicted in FIG. 7D, to increase the number of layers within a fixedvolume to increase the surface area per unit volume. The preload iscalculated by the formula:

$P = {1 - \left( \frac{h_{final}}{h_{start}} \right)}$where P is the Preload and h_(start) is the corrugation or flute heightprior to compression and wherein h_(final) is the height of thecorrugation post-compression.

Alternatively, the final three-dimensional shape of the HME 7000 may beformed by combining layers 7001 of different sizes and shapes to producea HME 7000 of irregular shape adapted to fit within a plenum chamber3200 of the patient interface 3000. The layers 7001 may be laser cut toform the desired shape and size.

As shown in FIG. 8A to 8D, displaying an alternative example, the HME7000 may be rolled from a single strip layer 7001 comprising acorrugated structure 7002 extending from the surface of the basestructure 7020 to form a plurality of corrugations 7030. The singlestrip layer 7001 may be rolled such that the upper folded portion 7031of the corrugations 7030 engages the inferior surface of the basestructure 7020. This configuration ensures that the plurality ofchannels 7012 is maintained between each roll of the single strip layer7001. The HME 7000 may be positioned within a plenum chamber 3200 of thepatient interface 3000.

FIGS. 9A to 9J, illustrate another example of the technology. Thepatient interface 3000 in this example has a removably engageablecushion assembly 3130 comprising a plurality of cushion assemblyengagement members 3135 in the form of a clip comprising a resilientflange that removably engages to a mask frame 3250. The mask frame 3250comprises a mask frame engagement member 3255 in the form of a recess orhole that allows for the resilient flange of the cushion assemblyengagement member 3135 to pass and removably engage thereto.Alternatively, the cushion assembly 3130 may engage to the mask frame byother methods such as hook, adhesive, interference or frictionalengagement. The cushion assembly 3130 comprises a seal forming structure3100. The seal forming structure 3100 may form a seal with the entranceof a patient's airways. In addition, the seal-forming structure 3100 ofthe patient interface 3000 may comprise a pair of nasal puffs, or nasalpillows, each nasal puff or nasal pillow being constructed and arrangedto form a seal with a respective naris of the nose of a patient.Alternatively, the seal forming structure may form a seal with the naresand the mouth.

The exemplary patient interface 3000 further comprises a removable HME7000 that removably engages with the patient interface 3000 and the HME7000 may be located within a HME housing portion 3420 of a vent adaptor3410. The HME 7000 may comprise at least one HME engagement member 7004positioned on the HME frame 7003. The at least one HME engagement member7004 may comprise a clip and each of which may removably engage acorresponding vent adaptor engagement member 3415. The vent adaptor 3410may comprise a vent 3400 and a mask inlet 3260 positioned on itsanterior side. The vent adaptor 3410 may be adapted to removably engageto the remainder of the patient interface 3000 and locate the removablyengageable HME 7000 within its HME housing portion 3420. The ventadaptor 3410 may locate the HME 7000 in a flow path of breathable gaswithin a plenum chamber 3200 of the patient interface 3000 and mayorient the plurality of channels 7012 and 7022 of the HME to besubstantially in line with or parallel to a flow path of the flow ofbreathable gas, thereby allowing flow through the HME via the channels7012 and 7022. The positioning of the HME 7000 in close proximity to theentrance of the patient's airways may maximise the capture and retentionof humidity that is provided to the material of the HME 7000 duringexhalation. Moreover, the orientation of the channels 7012, 7022 mayalso allow the flow of humidified gas exhaled from the patient to flowthrough the channels 7012 and 7022 of the HME in the opposing direction.

The vent adaptor 3410, shown in FIGS. 12A to 12D, may locate the HME7000 within the plenum chamber 3200 and may divide said plenum chamber3200 into an anterior plenum chamber 3240 and a posterior plenum chamber3230. This positioning of the HME 7000 may position the vent 3400 andinlet 3260 on an anterior side of the HME 7000 as part of the anteriorplenum chamber 3240 with the entrance of the patient's airways on aposterior side of the HME 7000, adjacent to the posterior plenum chamber3230. This configuration may allow the flow of exhaled gas from thepatient to flow into the posterior plenum chamber 3240 prior to venting,which allows any humidity to be retained in the HME 7000 prior to lossesout of the vent 3400. Furthermore, the configuration also may allow theflow of breathable gas to flow through the HME 7000 prior to redeliveryof the captured humidity to the patient. Thus, the housing portion 3410may provide a configuration for redelivering humidified air to a patientvia a HME 7000 positioned in the flow path of the patient interface3000.

The vent adaptor 3410 may also include receiving portions 3440 toreceive respective engagement members 7004 of the HME frame 7003. Thereceiving portions 3440 may releasably join with the engagement members7004 in a snap-fit. The vent adaptor 3410 may also include attachmentmembers 3450 to releasably join the vent adaptor 3410 to the mask frame3250. The attachment members 3450 may attach the vent adaptor 3410 tothe mask frame with snap-fit.

It is also possible to position an auxiliary vent 3401 on the posteriorside of the HME in the posterior plenum chamber 3240 to offset CO₂ buildup within this volume. For example, in the case of a full face mask, theadditional volume in the posterior plenum chamber 3240 (i.e., dead spacevolume) in comparison to smaller masks, may lead to unwanted and/orexcessive CO₂ build up occurring within this space. To mitigate thiseffect, it is possible to position an auxiliary vent 3401 proximal tothe patient's airways, on the posterior or patient side of the HME 7000.Positioning an auxiliary vent 3401 on the posterior side of the HME 7000will result in some venting of the humidified flow of breathable gasesprior to delivery to the patient. To compensate for this venting ofhumidified air, the overall humidification performance may be maintainedby increasing the ability of the HME 7000 to humidify the flow ofbreathable gas within a predetermined volume of the plenum chamber 3400.

The vent adaptor 3410 may also include a baffle 3430 to separate theincoming flow of breathable gas from the flow of CO₂ washout. The baffle3430 may separate these flows of gas from one another such that theseflows of gas do not interfere with one another. U.S. Pat. No. 7,934,501,which is incorporated herein by reference in its entirety, describesfurther examples and features of baffles that may be applicable to theexemplary patient interface 3000.

FIGS. 10 to 10F depict examples of the HME frame 7003 according to thepresent technology. The HME frame 7003 may include one or moreengagement member 7004. The engagement members 7004 may be releasablyengage with the vent adaptor 3410. Alternatively, the engagement members7004 may also allow the HME frame 7003 to be direct and releasablyengaged with the plenum chamber 3200 of the patient interface 3000 orthe mask frame 3250. The HME frame may include one or more frameapertures 7006 to allow the flow of breathable gas and/or the flow ofexhaled gas to pass through the frame apertures 7006 and through the HMElayers 7001. The HME frame 7003 may also include one or more HMEretention members 7005. The HME retention members 7005 may be hold theHME layers 7001 in place and the HME retention members 7005 may alsoprovide structural support for the HME frame 7003. The HME retentionmembers 7005 may be provided to the front and/or the rear of the HMEframe 7003. In the front and rear views shown in FIGS. 10A and 10B,respectively, the HME frame 7003 has a generally rectangular shape. Itshould be understood that the HME frame 7003 have other shapes as wellto provide for the most effective utilization of space within thepatient interface 3000. For example, the HME frame 7003 may have asquare, oval, circular, triangular, or other polygonal shape.Accordingly, the HME layers 7001 may be shaped to conform to theinterior shape of the HME frame 7003 depending on the shape of the HMEframe 7003. FIG. 10D shows a top view of the HME frame 7003 and in thisview it can be seen that the HME frame 7003 according to this example ofthe present technology is swept backwards at its lateral ends to accountfor the shape of the patient interface 3000. It should be understoodthat the HME frame 7003 may also have profile that is flat from thisview as well, or swept forwards, depending on the shape of the patientinterface 3000.

As is illustrated in FIGS. 1A to 11G, the HME 7000 may be stacked inlayers 7001 and further comprise a rigid supporting HME frame 7003. TheHME layers 7001 may be retained within the HME frame 7003 by one or moreHME retaining members 7005. The HME frame 7003 may comprise a frameaperture 7006 that is aligned with the plurality of channels 7012 and7022 that are defined by corrugations 7030 and run through the layers7001 of the HME 7000. The frame aperture 7006 allows the flow of gas toflow through the HME in both directions, which allows the exchange ofheat and moisture to be retained and redelivered to the patient. Theinwardly curved predetermined three-dimensional shape of the HME frame7003 is adapted to fit within the plenum chamber 3200 of the patientinterface 3000 and avoid contact with the patient's face when thepatient interface 3000 is positioned on the face. Other predeterminedthree-dimensional shapes may be provided to avoid contact with thepatient's face while maintaining the ability of the HME 7000 fit withinthe plenum chamber 3200 of the patient interface 3000.

FIG. 13A shows a flow diagram of an exemplary process that may befollowed for selecting a suitable heat and moisture exchanger (HME orHMX). The exemplary process may be used to test whether the HME is ableto attain desired parameters in relation to humidification performance.The process is adapted from ISO9360. The process involves simulating ahumidified lung and placing said lung in fluid communication with apatient interface under various testing conditions. The testingconditions may include:

-   -   i) No humidification    -   ii) Passive humidification using an in mask HME. A corrugated        HME comprising a plurality of layers was used comprising a        corrugated structure of F-Flute as shown in FIG. 13C with the        properties listed in FIG. 13D under ‘Tested HME (Flute F)’.    -   iii) Active humidification using a powered humidifier H5i at 23°        C., RH80%    -   iv) Active humidification using a powered humidifier H5i at 30°        C., RH80%

As shown in the exemplary results displayed in FIG. 13B, humidified lungweight loss was used as an indicator for simulating humidity lost in apatient's lungs under RPT therapy. As expected, no humidification i)showed the highest weight loss, simulating humidity lost by a patientunder RPT therapy without any added humidification. This may ultimatelylead to breathing discomfort. Passive humidification performed betterthan active humidification by a H5i at 23° C., RH80%. Passivehumidification was also close in performance to extreme humidificationusing a powered humidifier H5i at 30° C., RH80%. Testing was conductedunder ambient conditions of 15.5° C., RH30%. The HME used for testingwas under a preload of 6% with a surface area per unit volume of 5.4m²/m³ as per the properties listed in FIG. 13D under ‘Tested HME (FluteF)’.

FIG. 13C illustrates various corrugation or flute configurations formingthe corrugated structure comprised in the HME that are under no preload.The F-Flute may be used to form the corrugated structure comprising aplurality of corrugated layers of the HME. In a non-preloaded andassembled configuration, the corrugated structure may be formed ofcorrugated paper with a height of 0.9 mm and a paper grade of 65 gsm.

FIG. 13D shows the parameters of various corrugated structures accordingto examples of the present technology. The ‘Tested HME’ comprising aplurality of layers in an Flute F configuration was under a preload of6%. This configuration provided a HME with a total volume of 8360 mm³and a total surface area per unit volume of 5.42 m²/m³. The total flowimpedance was found to be 0.47 cmH₂O. The HME under optimal conditionsmay comprise 26 layers stacked under 32% preload to give a total volumeof 4560 mm³ and a surface area per unit volume of 7.5 m²/m³. The HME hasa flow impedance of 1.6 cmH₂O, which may provide a smaller HME withimproved humidification performance within an acceptable impedancerange. FIG. 13E illustrates the dimensions measured to provide theparameters listed in FIG. 13D. The corrugation perimeter is the lengthof paper material that forms a single corrugation or flute. As listed inFIG. 13D, this length is maintained between the tested HME and theoptimal HME as the preload is increased to compress the corrugation intoa smaller volume. The compressive force under preload is applied to thefolded portion of the corrugation to reduce the flute height whilemaintaining the flute pitch. The stack represents the plurality oflayers vertically stacked into the illustrated three-dimensional shape,wherein the stack height is reduced as the preload is increased, therebyincreasing the surface area per unit volume of the HME.

Examples of the technology are directed towards an HME 7000 positionedwithin the functional dead space of various full face patient interfaces3000 (see FIG. 14A to FIG. 14F, FIG. 15A to FIG. 15 , and FIG. 16 ). TheHME 7000 may be positioned in the plenum chamber 3200 such that itremains between the patient's 1000 airways and the mask vent 3400/inlet3260 of the patient interface 3000. The HME 7000 may be supported andheld in position by a supporting membrane 7050 that may be connected tothe inside walls of the plenum chamber 3200. The HME 7000 in theseexamples is circular in form and has a thickness of approximately 5-10mm. Alternatively, the HME material is moulded into a profiled shapewhich directly assembles to the interior profile of the plenum chamber3200, wherein the HME make take on a shape complementary to the interiorof the plenum chamber 3200. In this case the shape may be a threedimensional surface with a thickness of approximately 1-10 mm.

In an example of a non-invasive patient interface 3000 in accordancewith one aspect of the present technology, the patient interface 3000may comprises the following functional aspects: a seal-forming structure3100, a plenum chamber 3200, a HME 6000 positioned in the functionaldead space within the plenum chamber 3200, a supporting membrane 7050structure to hold the HME 7000 in position, a positioning andstabilising structure 3300 and a connection port or inlet 3260 forconnection to air circuit 4170. In some forms a functional aspect may beprovided by one or more physical components. In some forms, one physicalcomponent may provide one or more functional aspects. In use theseal-forming structure 3100 is arranged to surround an entrance to theairways of the patient so as to facilitate the supply of air at positivepressure to the airways.

A positioning and stabilising structure 3300 may also be provided toreleasably secure the patient interface 3000 to the patient 1000. Thepositioning and stabilising structure 3300 may include a plurality ofstraps that are adjustable in length to allow the patient interface tobe comfortably and securely fitted to the patient 1000 such that apneumatic seal is formed around the patient's airways by theseal-forming structure 3100. A strap connector 3301 may also be providedto releasably secure the straps of the positioning and stabilisingstructure 3300 to the patient interface 3000. The straps of thepositioning and stabilising structure 3300 may include hook and loopmaterial for length adjustment and to allow the straps of thepositioning and stabilising structure 3300 to be attached to anddetached from the strap connector 3301. It should be understood that thestrap connector 3301 may be releasably attached to the patient interface3000 or it may be integrally formed therewith.

The positioning of the HME 7000 within the patient interface may bealtered to adjust the hygroscopic performance. For example the distancebetween the HME and the airways of a patient 1000 may be adjusted.Moreover, the distance between the HME 7000 and the vent 3400 and/orinlet 3260 may also be adjusted. Adjusting the positioning of the HME7000 may alter the hygroscopic performance of the HME by adjusting theposition of the HME 7000 relative to the patient's 1000 airways. Thatis, the closer the HME 7000 is positioned to the patient's 1000 airwaysthe closer it is to the source of humidity during exhalation and to thetarget of humidification during inhalation. However, the HME 7000 may bepositioned such that it avoids contact with the patient's face.Similarly, adjusting the position of the HME 7000 may also impactimpedance on flow due to the positioning relative to the inlet 3260 andthe effect on CO₂ washout, impacted by relative position the vent 3400.By positioning the HME 7000 in the functional dead space of the patientinterface 3000, the HME may occupy a larger volume compared to thevolume the HME 7000 would occupy inside an air delivery conduit orelbow. This in turn may allow for more flexibility to position the HME7000 in a larger volume to minimise impedance on therapy flow and CO₂washout, while allowing for the maximisation of hygroscopic performance.While all the above benefits also apply to a moulded HME insert, the HMEinsert concept may provide greater design control and may reduce thetrade-off between contradictory functions. Similarly, the thickness andarea of the HME 7000 may also be varied to adjust these properties. Forexample, a HME 7000 with an increased surface area can have an increasedhygroscopic performance. Moreover, a HME 7000 that is thinner canincrease its permeability and therefore reduce impedance.

In these examples, the flexible supporting membrane 7050 may bepositioned to connect within the inside walls of the plenum chamber 3200and support the HME 7000 within the functional dead space of the patientinterface 3000. The flexible supporting membrane 7050 may be made of aflexible material such as silicone but could also be made from HMEmaterial. The flexibility allows for easily manipulating and moving theflexible supporting membrane 7050 holding the HME 7000. Furthermore, theflexible supporting membrane 7050 may be impermeable to humidified airexhaled from the patient's 1000 airways to avoid any loss inhumidification thorough the vent 3400. Impermeability of the flexiblesupporting membrane 7050 may ensure that the exhaled humidified airpasses through the HME 7000 for maximised hygroscopic performance.

In another example, a HME 7000 may be positioned in the functional deadspace within the plenum chamber 3200 of patient interface 3000 in theform of a nasal mask supported by a supporting membrane 7050.

In one example of the technology, the added humidity above ambienthumidity is measured using a Humiflo HME, as shown in FIG. 17 , having adiameter of 35 cm with a volume of 10 cm³. The HME is positioned in thefunctional dead space of a ResMed Quattro FX patient interface. It isnoted that leak at the patient interface can result in the increase ofaverage an flow rate through the plenum chamber of the patientinterface, ultimately having a negative impact by reducing the humiditywithin the patient interface due to loses though the system. The addedhumidity was measured at therapeutic pressures ranging from 4 cm of H₂Oto 20 cm of H₂O (flow rates ranging from 20 L/min to 50 L/min). FIG. 17shows an addition of approximately 5 mg/L to 18 mg/L of added absolutehumidity. More specifically, the graph shows an added absolute humidityof 9.5 mg/L to 17.5 mg/L at the same flow rates. The humidity over timeat a particular pressure ranges from a minimum humidity occurring duringinhalation and a maximum humidity during exhalation. The averagehumidity was measured across the breath cycle as a comparative metric.

5.8 Glossary

For the purposes of the present technology disclosure, in certain formsof the present technology, one or more of the following definitions mayapply. In other forms of the present technology, alternative definitionsmay apply.

5.8.1 General

Air: In certain forms of the present technology, air may be taken tomean atmospheric air, and in other forms of the present technology airmay be taken to mean some other combination of breathable gases, e.g.atmospheric air enriched with oxygen.

Ambient: In certain forms of the present technology, the term ambientwill be taken to mean (i) external of the treatment system or patient,and (ii) immediately surrounding the treatment system or patient.

For example, ambient humidity with respect to a humidifier may be thehumidity of air immediately surrounding the humidifier, e.g. thehumidity in the room where a patient is sleeping. Such ambient humiditymay be different to the humidity outside the room where a patient issleeping.

In another example, ambient pressure may be the pressure immediatelysurrounding or external to the body.

In certain forms, ambient (e.g. acoustic) noise may be considered to bethe background noise level in the room where a patient is located, otherthan for example, noise generated by a RPT device or emanating from amask or patient interface. Ambient noise may be generated by sourcesoutside the room.

Continuous Positive Airway Pressure (CPAP): CPAP treatment will be takento mean the application of a supply of air to the entrance to theairways at a pressure that is continuously positive with respect toatmosphere, and approximately constant through a respiratory cycle of apatient. In some forms, the pressure at the entrance to the airways willbe slightly higher during exhalation, and slightly lower duringinhalation. In some forms, the pressure will vary between differentrespiratory cycles of the patient, for example being increased inresponse to detection of indications of partial upper airwayobstruction, and decreased in the absence of indications of partialupper airway obstruction.

5.8.2 Aspects of the Respiratory Cycle

Apnea: Apnea will be said to have occurred when flow falls below apredetermined threshold for a duration, e.g. 10 seconds. An obstructiveapnea will be said to have occurred when, despite patient effort, someobstruction of the airway does not allow air to flow. A central apneawill be said to have occurred when an apnea is detected that is due to areduction in breathing effort, or the absence of breathing effort,despite the airway being patent. A mixed apnea occurs when a reductionor absence of breathing effort coincides with an obstructed airway.

Breathing rate: The rate of spontaneous respiration of a patient,usually measured in breaths per minute.

Duty cycle: The ratio of inhalation time, Ti to total breath time, Ttot.

Effort (breathing): Breathing effort will be said to be the work done bya spontaneously breathing person attempting to breathe.

Expiratory portion of a breathing cycle: The period from the start ofexpiratory flow to the start of inspiratory flow.

Flow limitation: Flow limitation will be taken to be the state ofaffairs in a patient's respiration where an increase in effort by thepatient does not give rise to a corresponding increase in flow. Whereflow limitation occurs during an inspiratory portion of the breathingcycle it may be described as inspiratory flow limitation. Where flowlimitation occurs during an expiratory portion of the breathing cycle itmay be described as expiratory flow limitation.

Types of flow limited inspiratory waveforms:

(i) Flattened: Having a rise followed by a relatively flat portion,followed by a fall.

(ii) M-shaped: Having two local peaks, one at the leading edge, and oneat the trailing edge, and a relatively flat portion between the twopeaks.

(iii) Chair-shaped: Having a single local peak, the peak being at theleading edge, followed by a relatively flat portion.

(iv) Reverse-chair shaped: Having a relatively flat portion followed bysingle local peak, the peak being at the trailing edge.

Hypopnea: A hypopnea will be taken to be a reduction in flow, but not acessation of flow. In one form, a hypopnea may be said to have occurredwhen there is a reduction in flow below a threshold for a duration. Acentral hypopnea will be said to have occurred when a hypopnea isdetected that is due to a reduction in breathing effort. In one form inadults, either of the following may be regarded as being hypopneas:

-   -   (i) a 30% reduction in patient breathing for at least 10 seconds        plus an associated 4% desaturation; or    -   (ii) a reduction in patient breathing (but less than 50%) for at        least 10 seconds, with an associated desaturation of at least 3%        or an arousal.

Hyperpnea: An increase in flow to a level higher than normal flow.

Inspiratory portion of a breathing cycle: The period from the start ofinspiratory flow to the start of expiratory flow will be taken to be theinspiratory portion of a breathing cycle.

Patency (airway): The degree of the airway being open, or the extent towhich the airway is open. A patent airway is open. Airway patency may bequantified, for example with a value of one (1) being patent, and avalue of zero (0), being closed (obstructed).

Positive End-Expiratory Pressure (PEEP): The pressure above atmospherein the lungs that exists at the end of expiration.

Peakflow (Qpeak): The maximum value of flow during the inspiratoryportion of the respiratory flow waveform.

Respiratoryflow, airflow, patient airflow, respiratory airflow (Qr):These synonymous terms may be understood to refer to the RPT device'sestimate of respiratory airflow, as opposed to “true respiratory flow”or “true respiratory airflow”, which is the actual respiratory flowexperienced by the patient, usually expressed in litres per minute.

Tidal volume (Vt): The volume of air inhaled or exhaled during normalbreathing, when extra effort is not applied.

(inhalation) Time (Ti): The duration of the inspiratory portion of therespiratory flow waveform.

(exhalation) Time (Te): The duration of the expiratory portion of therespiratory flow waveform.

(total) Time (Ttot): The total duration between the start of theinspiratory portion of one respiratory flow waveform and the start ofthe inspiratory portion of the following respiratory flow waveform.

Typical recent ventilation: The value of ventilation around which recentvalues over some predetermined timescale tend to cluster, that is, ameasure of the central tendency of the recent values of ventilation.

Upper airway obstruction (UAO): includes both partial and total upperairway obstruction. This may be associated with a state of flowlimitation, in which the level of flow increases only slightly or mayeven decrease as the pressure difference across the upper airwayincreases (Starling resistor behaviour).

Ventilation (Vent): A measure of the total amount of gas being exchangedby the patient's respiratory system, including both inspiratory andexpiratory flow, per unit time. When expressed as a volume per minute,this quantity is often referred to as “minute ventilation”. Minuteventilation is sometimes given simply as a volume, understood to be thevolume per minute.

5.8.3 RPT Device Parameters

Flow rate (orflow): The instantaneous volume (or mass) of air deliveredper unit time. While flow rate and ventilation have the same dimensionsof volume or mass per unit time, flow rate is measured over a muchshorter period of time. In some cases, a reference to flow rate will bea reference to a scalar quantity, namely a quantity having magnitudeonly. In other cases, a reference to flow rate will be a reference to avector quantity, namely a quantity having both magnitude and direction.Where it is referred to as a signed quantity, a flow rate may benominally positive for the inspiratory portion of a breathing cycle of apatient, and hence negative for the expiratory portion of the breathingcycle of a patient. Flow rate will be given the symbol Q. Total flow,Qt, is the flow rate of air leaving the RPT device. Vent flow, Qv, isthe flow rate of air leaving a vent to allow washout of exhaled gases.Leak flow, Ql, is the flow rate of unintentional leak from a patientinterface system. Respiratory flow, Qr, is the flow rate of air that isreceived into the patient's respiratory system.

Leak: The word leak will be taken to be a flow of air to the ambient.Leak may be intentional, for example to allow for the washout of exhaledCO₂. Leak may be unintentional, for example, as the result of anincomplete seal between a mask and a patient's face. In one example leakmay occur in a swivel elbow.

Noise, conducted (acoustic): Conducted noise in the present documentrefers to noise which is carried to the patient by the pneumatic path,such as the air circuit and the patient interface as well as the airtherein. In one form, conducted noise may be quantified by measuringsound pressure levels at the end of an air circuit.

Noise, radiated (acoustic): Radiated noise in the present documentrefers to noise which is carried to the patient by the ambient air. Inone form, radiated noise may be quantified by measuring soundpower/pressure levels of the object in question according to ISO 3744.

Noise, vent (acoustic): Vent noise in the present document refers tonoise which is generated by the flow of air through any vents such asvent holes in the patient interface.

Pressure: Force per unit area. Pressure may be measured in a range ofunits, including cmH₂O, g-f/cm², hectopascal. 1 cmH₂O is equal to 1g-f/cm² and is approximately 0.98 hectopascal. In this specification,unless otherwise stated, pressure is given in units of cmH₂. Thepressure in the patient interface is given the symbol Pm, while thetreatment pressure, which represents a target value to be achieved bythe mask pressure Pm at the current instant of time, is given the symbolPt.

Sound Power: The energy per unit time carried by a sound wave. The soundpower is proportional to the square of sound pressure multiplied by thearea of the wavefront. Sound power is usually given in decibels SWL,that is, decibels relative to a reference power, normally taken as 10⁻¹²watt.

Sound Pressure: The local deviation from ambient pressure at a giventime instant as a result of a sound wave travelling through a medium.Sound pressure is usually given in decibels SPL, that is, decibelsrelative to a reference pressure, normally taken as 20×10⁻⁶ Pascal (Pa),considered the threshold of human hearing.

5.8.4 Terms for Ventilators

Adaptive Servo-Ventilator: A ventilator that has a changeable, ratherthan fixed target ventilation. The changeable target ventilation may belearned from some characteristic of the patient, for example, arespiratory characteristic of the patient.

Backup rate: A parameter of a ventilator that establishes the minimumrespiration rate (typically in number of breaths per minute) that theventilator will deliver to the patient, if not otherwise triggered.

Cycled: The termination of a ventilator's inspiratory phase. When aventilator delivers a breath to a spontaneously breathing patient, atthe end of the inspiratory portion of the breathing cycle, theventilator is said to be cycled to stop delivering the breath.

EPAP (or EEP): a base pressure, to which a pressure varying within thebreath is added to produce the desired mask pressure which theventilator will attempt to achieve at a given time.

IPAP: desired mask pressure which the ventilator will attempt to achieveduring the inspiratory portion of the breath.

Pressure support: A number that is indicative of the increase inpressure during ventilator inspiration over that during ventilatorexpiration, and generally means the difference in pressure between themaximum value during inspiration and the minimum value during expiration(e.g., PS=IPAP−EPAP). In some contexts pressure support means thedifference which the ventilator aims to achieve, rather than what itactually achieves.

Servo-ventilator: A ventilator that measures patient ventilation has atarget ventilation, and which adjusts the level of pressure support tobring the patient ventilation towards the target ventilation.

Spontaneous/Timed (ST)—A mode of a ventilator or other device thatattempts to detect the initiation of a breath of a spontaneouslybreathing patient. If however, the device is unable to detect a breathwithin a predetermined period of time, the device will automaticallyinitiate delivery of the breath.

Swing: Equivalent term to pressure support.

Triggered: When a ventilator delivers a breath of air to a spontaneouslybreathing patient, it is said to be triggered to do so at the initiationof the respiratory portion of the breathing cycle by the patient'sefforts.

Ventilator A mechanical device that provides pressure support to apatient to perform some or all of the work of breathing.

5.8.5 Anatomy of the Face

Ala: the external outer wall or “wing” of each nostril (plural: alar)

Alare: The most lateral point on the nasal ala.

Alar curvature (or alar crest) point: The most posterior point in thecurved base line of each ala, found in the crease formed by the union ofthe ala with the cheek.

Auricle: The whole external visible part of the ear.

(nose) Bonyframework: The bony framework of the nose comprises the nasalbones, the frontal process of the maxillae and the nasal part of thefrontal bone.

(nose) Cartilaginousframework: The cartilaginous framework of the nosecomprises the septal, lateral, major and minor cartilages.

Columella: the strip of skin that separates the nares and which runsfrom the pronasale to the upper lip.

Columella angle: The angle between the line drawn through the midpointof the nostril aperture and a line drawn perpendicular to the Frankfurthorizontal while intersecting subnasale.

Frankfort horizontal plane: A line extending from the most inferiorpoint of the orbital margin to the left tragion. The tragion is thedeepest point in the notch superior to the tragus of the auricle.

Glabella: Located on the soft tissue, the most prominent point in themidsagittal plane of the forehead.

Lateral nasal cartilage: A generally triangular plate of cartilage. Itssuperior margin is attached to the nasal bone and frontal process of themaxilla, and its inferior margin is connected to the greater alarcartilage.

Greater alar cartilage: A plate of cartilage lying below the lateralnasal cartilage. It is curved around the anterior part of the naris. Itsposterior end is connected to the frontal process of the maxilla by atough fibrous membrane containing three or four minor cartilages of theala.

Nares (Nostrils): Approximately ellipsoidal apertures forming theentrance to the nasal cavity. The singular form of nares is naris(nostril). The nares are separated by the nasal septum.

Naso-labial sulcus or Naso-labialfold: The skin fold or groove that runsfrom each side of the nose to the corners of the mouth, separating thecheeks from the upper lip.

Naso-labial angle: The angle between the columella and the upper lip,while intersecting subnasale.

Otobasion inferior: The lowest point of attachment of the auricle to theskin of the face.

Otobasion superior: The highest point of attachment of the auricle tothe skin of the face.

Pronasale: the most protruded point or tip of the nose, which can beidentified in lateral view of the rest of the portion of the head.

Philtrum: the midline groove that runs from lower border of the nasalseptum to the top of the lip in the upper lip region.

Pogonion: Located on the soft tissue, the most anterior midpoint of thechin.

Ridge (nasal): The nasal ridge is the midline prominence of the nose,extending from the Sellion to the Pronasale.

Sagittal plane: A vertical plane that passes from anterior (front) toposterior (rear) dividing the body into right and left halves.

Sellion: Located on the soft tissue, the most concave point overlyingthe area of the frontonasal suture.

Septal cartilage (nasal): The nasal septal cartilage forms part of theseptum and divides the front part of the nasal cavity.

Subalare: The point at the lower margin of the alar base, where the alarbase joins with the skin of the superior (upper) lip.

Subnasal point: Located on the soft tissue, the point at which thecolumella merges with the upper lip in the midsagittal plane.

Supramentale: The point of greatest concavity in the midline of thelower lip between labrale inferius and soft tissue pogonion

5.8.6 Anatomy of the Skull

Frontal bone: The frontal bone includes a large vertical portion, thesquama frontalis, corresponding to the region known as the forehead.

Mandible: The mandible forms the lower jaw. The mental protuberance isthe bony protuberance of the jaw that forms the chin.

Maxilla: The maxilla forms the upper jaw and is located above themandible and below the orbits. The frontal process of the maxillaprojects upwards by the side of the nose, and forms part of its lateralboundary.

Nasal bones: The nasal bones are two small oblong bones, varying in sizeand form in different individuals; they are placed side by side at themiddle and upper part of the face, and form, by their junction, the“bridge” of the nose.

Nasion: The intersection of the frontal bone and the two nasal bones, adepressed area directly between the eyes and superior to the bridge ofthe nose.

Occipital bone: The occipital bone is situated at the back and lowerpart of the cranium. It includes an oval aperture, theforamen magnum,through which the cranial cavity communicates with the vertebral canal.The curved plate behind the foramen magnum is the squama occipitalis.

Orbit: The bony cavity in the skull to contain the eyeball.

Parietal bones: The parietal bones are the bones that, when joinedtogether, form the roof and sides of the cranium.

Temporal bones: The temporal bones are situated on the bases and sidesof the skull, and support that part of the face known as the temple.

Zygomatic bones: The face includes two zygomatic bones, located in theupper and lateral parts of the face and forming the prominence of thecheek.

5.8.7 Anatomy of the Respiratory System

Diaphragm: A sheet of muscle that extends across the bottom of the ribcage. The diaphragm separates the thoracic cavity, containing the heart,lungs and ribs, from the abdominal cavity. As the diaphragm contractsthe volume of the thoracic cavity increases and air is drawn into thelungs.

Larynx: The larynx, or voice box houses the vocal folds and connects theinferior part of the pharynx (hypopharynx) with the trachea.

Lungs: The organs of respiration in humans. The conducting zone of thelungs contains the trachea, the bronchi, the bronchioles, and theterminal bronchioles. The respiratory zone contains the respiratorybronchioles, the alveolar ducts, and the alveoli.

Nasal cavity: The nasal cavity (or nasal fossa) is a large air filledspace above and behind the nose in the middle of the face. The nasalcavity is divided in two by a vertical fin called the nasal septum. Onthe sides of the nasal cavity are three horizontal outgrowths callednasal conchae (singular “concha”) or turbinates. To the front of thenasal cavity is the nose, while the back blends, via the choanae, intothe nasopharynx.

Pharynx. The part of the throat situated immediately inferior to (below)the nasal cavity, and superior to the oesophagus and larynx. The pharynxis conventionally divided into three sections: the nasopharynx(epipharynx) (the nasal part of the pharynx), the oropharynx(mesopharynx) (the oral part of the pharynx), and the laryngopharynx(hypopharynx).

5.8.8 Materials

Silicone or Silicone Elastomer: A synthetic rubber. In thisspecification, a reference to silicone is a reference to liquid siliconerubber (LSR) or a compression moulded silicone rubber (CMSR). One formof commercially available LSR is SILASTIC (included in the range ofproducts sold under this trademark), manufactured by Dow Corning.Another manufacturer of LSR is Wacker. Unless otherwise specified to thecontrary, a form of LSR has a Shore A (or Type A) indentation hardnessin the range of about 35 to about 45 as measured using ASTM D2240.

Polycarbonate: a typically transparent thermoplastic polymer ofBisphenol-A Carbonate.

5.8.9 Aspects of a Patient Interface

Anti-asphyxia valve (AA V): The component or sub-assembly of a masksystem that, by opening to atmosphere in a failsafe manner, reduces therisk of excessive CO₂ rebreathing by a patient.

Elbow: A conduit that directs an axis of flow of air to change directionthrough an angle. In one form, the angle may be approximately 90degrees. In another form, the angle may be less than 90 degrees. Theconduit may have an approximately circular cross-section. In anotherform the conduit may have an oval or rectangular cross-section.

Mask Frame: Mask frame will be taken to mean a mask structure that bearsthe load of tension between two or more points of connection with aheadgear. A mask frame may be a non-airtight load bearing structure inthe mask. However, some forms of mask frame may also be air-tight.

Headgear. Headgear will be taken to mean a form of positioning andstabilizing structure designed for use on a head. The headgear maycomprise a collection of one or more struts, ties and stiffenersconfigured to locate and retain a patient interface in position on apatient's face for delivery of respiratory therapy. Some ties are formedof a soft, flexible, elastic material such as a laminated composite offoam and fabric.

Membrane: Membrane will be taken to mean a typically thin element thathas substantially no resistance to bending, but has resistance to beingstretched.

Plenum chamber: a mask plenum chamber will be taken to mean a portion ofa patient interface having walls enclosing a volume of space, the volumehaving air therein pressurised above atmospheric pressure in use. Ashell may form part of the walls of a mask plenum chamber.

Seal: The noun form (“a seal”) will be taken to mean a structure orbarrier that intentionally resists the flow of air through the interfaceof two surfaces. The verb form (“to seal”) will be taken to mean toresist a flow of air.

Shell: A shell will be taken to mean a curved two-dimensional structurehaving bending, tensile and compressive stiffness, for example, aportion of a mask that forms a curved structural wall of the mask.Compared to its overall dimensions, it is relatively thin. In someforms, a shell may be faceted. Such walls may be airtight, although insome forms they may not be airtight.

Stiffener: A stiffener will be taken to mean a structural componentdesigned to increase the bending resistance of another component in atleast one direction.

Strut: A strut will be taken to be a structural component designed toincrease the compression resistance of another component in at least onedirection.

Swivel: (noun) A subassembly of components configured to rotate about acommon axis, independently, and under low torque. In one form, theswivel may be constructed to rotate through an angle of at least 360degrees. In another form, the swivel may be constructed to rotatethrough an angle less than 360 degrees. When used in the context of anair delivery conduit, the sub-assembly of components comprises a matchedpair of cylindrical conduits. There is little or no leak flow of airfrom the swivel in use.

Tie: A tie will be taken to be a structural component designed to resisttension.

Vent: (noun) the structure that allows an intentional flow of air froman interior of the mask, or conduit to ambient air, e.g. to allowwashout of exhaled gases.

5.8.10 Terms Used in Relation to Patient Interface

Curvature (of a surface): A region of a surface having a saddle shape,which curves up in one direction and curves down in a differentdirection, will be said to have a negative curvature. A region of asurface having a dome shape, which curves the same way in two principaldirections, will be said to have a positive curvature. A flat surfacewill be taken to have zero curvature.

Floppy: A quality of a material, structure or composite that is one ormore of:

-   -   Readily conforming to finger pressure.    -   Unable to retain its shape when caused to support its own        weight.    -   Not rigid.    -   Able to be stretched or bent elastically with little effort.

The quality of being floppy may have an associated direction, hence aparticular material, structure or composite may be floppy in a firstdirection, but stiff or rigid in a second direction, for example asecond direction that is orthogonal to the first direction.

Resilient: Able to deform substantially elastically, and to releasesubstantially all of the energy upon unloading, within a relativelyshort period of time such as 1 second.

Rigid: Not readily deforming to finger pressure, and/or the tensions orloads typically encountered when setting up and maintaining a patientinterface in sealing relationship with an entrance to a patient'sairways.

Semi-rigid: means being sufficiently rigid to not substantially distortunder the effects of mechanical forces typically applied during positiveairway pressure therapy.

5.9 Other Remarks

A portion of the disclosure of this patent document contains materialwhich is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent file or records, but otherwise reserves all copyrightrights whatsoever.

Unless the context clearly dictates otherwise and where a range ofvalues is provided, it is understood that each intervening value, to thetenth of the unit of the lower limit, between the upper and lower limitof that range, and any other stated or intervening value in that statedrange is encompassed within the technology. The upper and lower limitsof these intervening ranges, which may be independently included in theintervening ranges, are also encompassed within the technology, subjectto any specifically excluded limit in the stated range. Where the statedrange includes one or both of the limits, ranges excluding either orboth of those included limits are also included in the technology.

Furthermore, where a value or values are stated herein as beingimplemented as part of the technology, it is understood that such valuesmay be approximated, unless otherwise stated, and such values may beutilized to any suitable significant digit to the extent that apractical technical implementation may permit or require it.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this technology belongs. Although any methods andmaterials similar or equivalent to those described herein can also beused in the practice or testing of the present technology, a limitednumber of the exemplary methods and materials are described herein.

When a particular material is identified as being used to construct acomponent, obvious alternative materials with similar properties may beused as a substitute. Furthermore, unless specified to the contrary, anyand all components herein described are understood to be capable ofbeing manufactured and, as such, may be manufactured together orseparately.

It must be noted that as used herein and in the appended claims, thesingular forms “a”, “an”, and “the” include their plural equivalents,unless the context clearly dictates otherwise.

All publications mentioned herein are incorporated by reference todisclose and describe the methods and/or materials which are the subjectof those publications. The publications discussed herein are providedsolely for their disclosure prior to the filing date of the presentapplication. Nothing herein is to be construed as an admission that thepresent technology is not entitled to antedate such publication byvirtue of prior invention. Further, the dates of publication providedmay be different from the actual publication dates, which may need to beindependently confirmed.

The terms “comprises” and “comprising” should be interpreted asreferring to elements, components, or steps in a non-exclusive manner,indicating that the referenced elements, components, or steps may bepresent, or utilized, or combined with other elements, components, orsteps that are not expressly referenced.

The subject headings used in the detailed description are included onlyfor the ease of reference of the reader and should not be used to limitthe subject matter found throughout the disclosure or the claims. Thesubject headings should not be used in construing the scope of theclaims or the claim limitations.

Although the technology herein has been described with reference toparticular examples, it is to be understood that these examples aremerely illustrative of the principles and applications of thetechnology. In some instances, the terminology and symbols may implyspecific details that are not required to practice the technology. Forexample, although the terms “first” and “second” may be used, unlessotherwise specified, they are not intended to indicate any order but maybe utilised to distinguish between distinct elements. Furthermore,although process steps in the methodologies may be described orillustrated in an order, such an ordering is not required. Those skilledin the art will recognize that such ordering may be modified and/oraspects thereof may be conducted concurrently or even synchronously.

It is therefore to be understood that numerous modifications may be madeto the illustrative examples and that other arrangements may be devisedwithout departing from the spirit and scope of the technology.

The invention claimed is:
 1. A patient interface for sealed delivery ofa flow of air at a continuously positive pressure with respect toambient air pressure to an entrance to a patient's airways including atleast the patient's nares, the patient interface being configured tomaintain a therapeutic pressure in a range of about 4 cmH2O to about 30cmH2O above ambient air pressure in use, throughout the patient'srespiratory cycle, while the patient is sleeping, to ameliorate sleepdisordered breathing, said patient interface comprising: a plenumchamber configured to be pressurised at the therapeutic pressure in use;a seal forming structure connected to the plenum chamber and configuredto seal with an area around the entrance to the patient's airwaysincluding at least the patient's nares, and the seal forming structurebeing constructed from a soft, flexible, resilient material; apositioning and stabilising structure comprising a plurality of strapsconfigured to maintain the seal forming structure in sealing contactwith the area surrounding the entrance to the patient's airways whilemaintaining the therapeutic pressure at the entrance to the patient'sairways; a connection port configured to connect to an air circuit toreceive the flow of air and direct the flow of air into the plenumchamber; a heat and moisture exchanger (HME) including an HME materialconfigured to absorb and retain moisture from a first portion of a flowof patient-exhaled gas and release moisture into the flow of air duringuse; a gas washout vent configured to be positioned opposite the patientrelative to the HME in use to allow the first portion of the flow ofpatient-exhaled gas to escape to ambient air after passing through theHME to minimise rebreathing of carbon dioxide by the patient; and anauxiliary vent configured to allow a second portion of the flow ofpatient-exhaled gas to escape to ambient air without passing through theHME to minimise rebreathing of carbon dioxide by the patient.
 2. Thepatient interface of claim 1, wherein the HME includes a rigid frame,the HME material being positioned within the rigid frame.
 3. The patientinterface of claim 2, wherein the rigid frame further comprises at leastone retention member configured to hold the HME material within therigid frame.
 4. The patient interface of claim 3, wherein the at leastone retention member is configured to structurally support the rigidframe.
 5. The patient interface of claim 3, further comprising a firstretention member positioned on a front side of the rigid frame and asecond retention member positioned on a rear side of the rigid frame. 6.The patient interface of claim 2, wherein the rigid frame includes atleast one engagement member configured to releasably attach the rigidframe to the patient interface.
 7. The patient interface of claim 6,wherein the at least one engagement member is configured to releasablyattach the rigid frame to the patient interface with a snap-fit.
 8. Thepatient interface of claim 2, wherein the rigid frame further comprisesat least one frame aperture oriented to allow the flow of air and/or thefirst portion of the flow of patient-exhaled gas to reach the HMEmaterial.
 9. The patient interface of claim 8, wherein the HME materialincludes a plurality of channels configured to allow the flow of air andthe first portion of the flow of patient-exhaled gas to pass through theHME material along a flow path, and wherein the at least one frameaperture is aligned with the flow path such that the flow of air and thefirst portion of the flow of patient-exhaled gas pass through the atleast one frame aperture during use.
 10. The patient interface of claim2, wherein the HME material is positioned such that during use: the flowof air travels in a first direction from the connection port, throughthe HME material, and to the patient's airways; and the first portion ofthe flow of patient-exhaled gas travels in a second direction, oppositethe first direction, from the patient's airways, through the HMEmaterial, and exits to atmosphere through the gas washout vent.
 11. Thepatient interface of claim 10, further comprising a baffle configured toseparate the flow of air traveling in the first direction from the firstportion of the flow of patient-exhaled gas traveling in the seconddirection.
 12. The patient interface of claim 2, wherein the HMEmaterial consists of foam.
 13. The patient interface of claim 2, whereinthe HME material consists of paper.
 14. The patient interface of claim13, wherein the paper HME material includes corrugations and the paperHME material is rolled into a coil.
 15. The patient interface of claim2, wherein the HME material comprises at least one of foam and paper.16. The patient interface of claim 1, wherein the HME material comprisesa plurality of layers arranged into a predetermined three-dimensionalshape.
 17. The patient interface of claim 1, wherein the HME materialcomprises a corrugated structure comprising a plurality of corrugations,the plurality of corrugations forming a plurality of channels to allowthe flow of air along a surface of the corrugated structure for moistureexchange.
 18. The patient interface of claim 17, wherein the HME isoriented such that the plurality of channels are substantially parallelto a flow path of the flow of air.
 19. The patient interface of claim 1,wherein the auxiliary vent is formed on the plenum chamber.
 20. Thepatient interface of claim 1, wherein the HME is positioned inside ofthe plenum chamber.
 21. The patient interface of claim 1, wherein thegas washout vent comprises a plurality of vent holes and the auxiliaryvent comprises a plurality of auxiliary vent holes.
 22. The patientinterface of claim 1, wherein the gas washout vent is positioned in theplenum chamber.
 23. The patient interface of claim 1, further comprisinga decoupling structure, the gas washout vent being positioned in thedecoupling structure.
 24. The patient interface of claim 1, wherein theauxiliary vent is configured to be positioned between the HME and thepatient in use.
 25. The respiratory therapy system of claim 24, whereinthe respiratory therapy system does not include a humidifier.
 26. Arespiratory therapy system to provide respiratory therapy to a patient,the respiratory therapy system comprising: a respiratory therapy deviceincluding a pressure generator configured to generate the flow of air atthe continuously positive pressure with respect to ambient air pressurein the range of about 4 cmH2O to about 30 cmH2O above ambient airpressure in use; the patient interface of claim 1; and an air circuitconfigured to direct the flow of air from the respiratory therapy deviceto the patient interface.